Setting Bullet Jump/Freebore for Accuracy

[Get Off My Lawn]

https://precisionrifleblog.com/2020/03/21/bullet-jump-and-seating-depth-reloading-best-practices/
Bullet Jump & Seating Depth: Best Practices & Conventional Wisdom
With so many events canceled and stores closed, what a great time to do some reloading! Over the past several weeks, I have been working on a series of posts that I’m very excited to finally share with you guys!

This article provides a comprehensive overview of what most professionally published books and reloading manuals suggest about bullet jump and seating depth when it comes to precision rifles. I have a big stack of books on the subject, and I tried to combine the most relevant info from each of them when it comes to fine-tuning the seating depth of your ammo.

What Is “Bullet Jump”?
Bullet jump is basically the distance a bullet travels before it touches the rifling in the barrel. That gap is relatively short distance that typically ranges from 0 to 0.150 inches, although it could be longer in some factory or magazine-fed rifles.

There is a lot going on in a chamber in the tiny window when a round goes off. Factors like whether the bullet jumps 0.010” or 0.070” before it engages the rifling may seem inconsequential but can have measurable impact on the bullet’s flight and group size. There are multiple reasons for that, which I’ll touch on from a high level below. But suffice to say that these kinds of details are especially relevant in shooting disciplines that are pushing the envelope of precision and/or engaging small targets at long distance.

There are two primary ways to fine-tune bullet jump:

1. Adjust Bullet Seating Depth: When handloading ammo, you can control how far the bullet must jump by adjusting bullet seating depth. However, when a reloader adjusts their seating depth to extend the bullet further out it increases the Cartridge Overall Length (COAL), which may prevent a loaded round from fitting inside your magazine. So, if feeding from a magazine is a priority, you could be limited on how close to the lands you can get.
2. Adjust Chamber Freebore: Another way to get a bullet closer to the lands and stay within magazine length is to shorten the throat of a chamber. Instead of extending the bullet out of the case towards the rifling by adjusting seating depth, you effectively move the rifling closer to the bullet. The diagram above shows an area labeled as “Throat,” but that distance is also commonly referred to as freebore. Freebore is simply the distance between the neck and where the rifling starts. Let’s say for example that the SAAMI chamber for a particular cartridge calls for 0.180” of freebore. If we use a chamber reamer that only had 0.100” of freebore, that would effectively move the rifling back towards the bullet 0.080”. Okay, technically it isn’t “moving” the rifling – it just means the chamber reamer would leave more of the rifling close to the chamber.

What Every Gunsmith Wish You Knew
Some shooters obsess over freebore (including me at times), and occasionally insist on specific freebore dimension for their barrel, despite a gunsmith’s recommendations. A gunsmith who is brutally honest might say that is one of the most annoying parts of their job. I feel like I should say that out loud on behalf of all my gunsmith friends. And I admit I’ve been an offender at times, too. While freebore can be an important spec, one of the best pieces of advice I can give is this: Find a gunsmith who specializes in precision rifles and has a proven track record of satisfied customers, then tell them what your goals are and how you plan to use the rifle, and finally: trust their recommendations.

What Are Recommended Best Practices When It Comes to Bullet Jump?

“It’s pretty well accepted that the shorter the gap, the better, and a long-held, and for good reason, accuracy-enhancing tactic is nearly or completely eliminating jump. The longer the bullet is, and the ‘spikier’ its nosecone, the better it will perform moving toward the lands.” – Glen Zediker, Top-Grade AMMO (Published 2016)

I’ve seen countless quotes like the one above in reloading manuals and books. Top-Grade Ammo is one of the best handloading resources I’ve read, but here is how another popular book explains it:


“Handloaders can tinker with the bullet-seating depth so as to exceed the listed maximum [cartridge overall length] significantly. Sometimes they can tinker until the bullet comes very close to touching the rifling. This can dramatically improve accuracy. When COAL places the bullet close to touching the rifling, changes of about 0.005 inch can dramatically alter accuracy. … For most hunting rifles and bullets, the optimum bullet-to-rifling jump is usually near 0.020 inch; for target cartridges used in target-chambered guns, the ideal jump can be near zero.” – Mic McPherson, Metallic Cartridge Handloading: Pursuit of the Perfect Cartridge


Glen Zediker wrote a book entitled Handloading for Competition: Making The Target Bigger, and here are some of the highlights from what it says about bullet jump and seating depth: “Determining the bullet seating depth a rifle likes best is normally ‘fine tuning’ that entices any stray holes to relocate on into the group. Any and every load and bullet responds to seating depth tuning. … How much jump is a good question that has only one answer: whatever shoots best. That may not be the answer anyone was looking for but it’s the right one, and it’s also not always the one we want to accept for various reasons. Most competition rifles will shoot best with bullets seated somewhere between jammed 0.020 and jumping 0.020. … Again, there is no fast rule on the amount of jump a particular combination will prefer, but odds are closer will do better.”

One of the most interesting articles I’ve ever read about precision shooting was called “Secrets of the Houston Warehouse.” It was written by Dave Scott and published by Precision Shooting Magazine in 1993. It’s about an accomplished group of Benchrest shooters who conducted experiments in a large warehouse that redefined extreme rifle accuracy. They used the large, controlled environment where the wind never blew, and mirage never shimmered to test virtually every aspect of rifle building and reloading. They were shooting 5-shot groups “in the zeros,” meaning the extreme spread measured 0.099” or less. In fact, they eventually fired 5-shot groups as small as 0.025”!!! Those experiments contributed to many of the best practices Benchrest shooters still use today, and here is what that article says about bullet jump:

“One thing that IS important is that the bullet be precisely seated against the lands. T.J. Jackson reported this fact in the May 1987 issue of Precision Shooting. In a letter to the Editor, T.J. wrote, “… in all our testing in that Houston warehouse … and the dozens and dozens of groups that Virgil King shot in there ‘in the zeroes’… he NEVER fired a single official screamer group when he was ‘jumping’ bullets. All his best groups were always seated into the lands, or at the very least … touching the lands.” – Secrets of The Houston Warehouse, Precision Shooting Magazine

 

[Get Off My Lawn]

Most published materials on reloading repeat a similar idea. The Hornady Reloading Manual simply says, “In general, the less distance to the bore, the greater the accuracy.”


Another one of my favorite resources are the books by Nathan Foster, an accomplished gunsmith in New Zealand and author of Terminal Ballistics Research. I’ve read a ton of what he’s written, and Nathan has earned my respect because he has both a practical and data-driven approach. Here is what Nathan says on the subject: “Why seat close to the lands? In our last example Joe read an article where the author stated that for best accuracy, he should be seating close to the lands. Many of you will have heard this statement. Target shooters often go to the extreme and wedge the projectiles right into the lands – but why? The statement ‘because it is more accurate this way’ is not really an explanation. Current research suggests that by pushing the projectile into the lands pressures can be made more consistent from shot to shot.” Nathan later adds that, “The projectile may arrive at the lands slightly off center if it has to travel a long way. In this instance, having the bullet close and concentric to the bore can help minimize potential bullet yaw during ignition. Close seating can also simply be used as a start point for harmonic experimentation. We can test the bullet up close to the lands, then step back if need be, monitoring the effects on accuracy.” So, Nathan has more a pragmatic approach, as expected, where he starts close and then experiments to see what jump results in the best accuracy for that rifle/bullet combination.


Dr. Harold Vaughn, who is literally one of the greatest researchers of the past 100 years (you should read about him here), concurs with the Nathan’s point about how important it is to get the bullet absolutely centered with the bore. In his book, Rifle Accuracy Facts, which covers his extensive research, he shares how Benchrest shooters desire chambers with minimum clearance in the necks and they also turn the necks of their brass to ensure the bullet is perfectly centered with the bore. Dr. Vaughn goes on to explain, “They also seat the bullets into the lands, which helps center the bullet. However, seating the bullet in the case so that it contacts the rifling in the throat also increase the peak chamber pressure, which is not desirable. Evidently the Benchrest shooters have found that having the bullet centered in the bore is important, and I think they are right. … Seating depth of the bullet in the case has an effect on just how close to the center the bullet will line up. Obviously, the bullet will be centered if it is in complete contact with the lands, however Reference 1 showed that peak chamber pressure decreases if the bullet has a free run before it contacts the lands. Since a minimum in peak pressure for a given load implies minimum bullet distortion, the author prefers a seating depth that will provide about 0.010 inches into the lands in the case of a Benchrest gun with light bullets and about 0.020 inches of bullet free travel before the bullet contacts the lands in the case of a sport shooting heavy bullets.”


Tony Boyer is the most successful and celebrated Benchrest shooter of all time. He has won several World Championships and was named Shooter of the Year over ten times. In his 2010 book, The Book of Rifle Accuracy, he simply says “When shooting with the bullet into the lands, the lands themselves straighten the bullet without forcing over-travel.” However, Tony goes on to say that bullet shape can affect optimal seating depth, and “There are no hard and fast rules dictating the best seating depth for all bullet/barrel combinations.” But, Tony does say there are some common characteristics of barrels, and when he’s searching for the sweet spot “with a button-rifled barrel such as a Shilen, I would have stopped the search for the optimal seating depth at the 0.012 inches off the jam. … With a four-groove cut-rifled barrel (Bartlein or Krieger), be more patient and keep trying until there is no mark on the bullet at all. Again, I personally do not want to shoot off the rifling so that become my stop point.” So, the guy who has proven several times that he can shoot the smallest groups in the world, says he is always at least touching the lands, and often the bullet is jammed into it.


“Now and then, 2-3 thousandths change in seating depth can make the difference between average and peak accuracy,” explains Mike Ratigan, Benchrest Hall of Famer and World Champion, in Extreme Rifle Accuracy. Wow, 0.002-0.003 inches in bullet jump can sometimes make the difference! Of the dozen or so published resources I’ve cited so far (plus others), they virtually all suggest testing seating depths in 0.005” increments, meaning most expect that changing the seating depth by just 0.005 inches or less can have a measurable impact on group size on the target.

I could cite even more books, but it seems like there is overwhelming support that if the absolute smallest groups are your highest priority, then minimizing jump seems to be the way to go. Everyone from accomplished scientific researchers to the absolute best-of-the-best, world-champion shooters are convinced that you’ll likely find the best accuracy with 0.020 inches of bullet jump or less.

The One Resource That Suggests Testing Longer

The only professionally published resource I’ve found that clearly recommends testing beyond 0.020” of bullet jump in a precision rifle is from Berger Bullets. In the Berger Bullets Reloading Manual they say:

“What has been discovered is that VLD bullets shoot best when loaded to a COAL that puts the bullet in a ‘sweet spot.’ This sweet spot is a band 0.030 to 0.040 wide, and is located anywhere between jamming the bullets into the lands and 0.150 jump off the lands.”

Berger’s VLD bullets are Very Low Drag bullets that have extremely high ballistic coefficients, meaning they are very aerodynamic and ideal for long range shooting, but have been known to be sensitive to seating depth (and probably more precisely bullet jump). Because VLD bullets were known to be very sensitive to bullet jump, Berger apparently performed a lot of research and found that the sweet spot for optimal precision could be as far as 0.150” of bullet jump on some rifles.

Eric Stecker, previously Master Bulletsmith for Berger and now President, provides detailed instructions for how to find the optimal jump in as few of shots as possible in their manual, but they also republished similar information in this article online: Getting the Best Precision and Accuracy from VLD bullets in Your Rifle.

 

[Tim]

I was skeptical about this until seeing it myself first hand. Messing with freebore on a Savage that another forum member now owns, made a .75 MOA gun a legit sub .5 MOA.

 

[Get Off My Lawn]

I was skeptical about this until seeing it myself first hand. Messing with freebore on a Savage that another forum member now owns, made a .75 MOA gun a legit sub .5 MOA.

My Sako 7-08 has a l-o-n-g freebore. The best 100yrd groups using top shelf Winchester, Federal and Hornady ammo was 2.75"!
The first handloads I made on my new 550 (in 2000) and setting the freebore to 0.005"-0.008" produced a 5 round 0.355"group using a traffic cone as a rifle rest. Thankfully they still fit in the magazine, the rounds were 1/4" longer than the factory ammo.

 

[jimmyjames8]

Great references in the OP. I just did a test load with 200.20X bergers in 308. Got load data from a thread on Accurate Shooter. Cant remember this second whether it was 0.010" jam or jump but what made the difference for me was getting an accurate measurement of where the bullet touches the lands. Ive tried lots of methods and tools. THis is the only thing that works for me:

 

[Precision Seeker]

Great references in the OP. I just did a test load with 200.20X bergers in 308. Got load data from a thread on Accurate Shooter. Cant remember this second whether it was 0.010" jam or jump but what made the difference for me was getting an accurate measurement of where the bullet touches the lands. Ive tried lots of methods and tools. THis is the only thing that works for me:

So the video has me intrigued about trying to hone in my distance to the lands using the described method.
Here's my conundrum...I do not currently own or have access to an ejector removal tool.
Any recommendations on one over another? Most of the ones I have seen are the Sinclair ones - $35-ish.
There's also a "complete" bolt tool kit for another $100. Is it worth it to have all of those tools?
I appreciate any words of wisdom or direction based on your collective experiences.
Thanks!

 

[Get Off My Lawn]

So the video has me intrigued about trying to hone in my distance to the lands using the described method.
Here's my conundrum...I do not currently own or have access to an ejector removal tool.
Any recommendations on one over another? Most of the ones I have seen are the Sinclair ones - $35-ish.
There's also a "complete" bolt tool kit for another $100. Is it worth it to have all of those tools?
I appreciate any words of wisdom or direction based on your collective experiences.
Thanks!

What type of bolt/gun is this tool needed for?

 

[Goofyfoot2001]

Coincidently loaded up a few 300 win mag extra long that of course won't fit in the mag. 230gr sitting next to the plain bullet and a 300blk in 220gr

 

[Precision Seeker]

What type of bolt/gun is this tool needed for?

Bergara BMP, so Rem 700 stuff should work

 

[Get Off My Lawn]

A second article just came out: https://precisionrifleblog.com/2020/04/15/18-shot-bullet-jump-challenge/
Add to that: https://precisionrifleblog.com/how-to-measure-the-distance-to-the-lands-on-your-rifle-barrel/
Mark’s 18-Shot Bullet Jump Challenge!
Are you one of those guys who has been reading this series of posts on bullet jump, and thinking to yourself, “Well, my 0.020” bullet jump sure seems to be working fine. Doubt this would be any improvement over what I’ve already got!” This is the post for you!

As Mark started sharing some of his bullet jump findings with a few shooters, he met some skepticism – even from sponsored shooters on his Short Action Customs team. Here is how Mark tells one of those stories:
Mark said this was originally a 15-shot challenge, where they shot 5 shots at each jump. But they eventually changed it to an 18-shot challenge by adding a 6th shot to each group because a slightly larger sample size was helpful to prevent false-positives and ensure they could have full confidence in the results.

For each jump, you’ll test a 0.010” wide window of bullet jumps. 0.010” is about much the lands of a barrel would likely erode over 200 rounds for most mid-sized cartridges that are common in precision rifle competitions (like Creedmoor, Dasher, or x47 Lapua cartridges). So unless you are going to adjust your seating depth every 100 rounds or less, you likely need to find a range of jumps that is at least that wide and provides a similar vertical point of impact (POI) across the entire range. That is what this challenge is designed to inform you about.

There are 18 shots per group, and you’ll end up firing 3 groups – for a total of 54 shots. But, at the end of those 54 shots, Mark feels like you’ll have hard data on whether your shorter jump is really better in realistic scenarios. Here are the groups and number of shots Mark recommends:

1. Group #1: 0.015-0.025” Bullet Jumps
   1. 6 shots at 0.015”
   1. 6 shots at 0.020”
   1. 6 shots at 0.025”
2. Group #2: 0.050-0.060” Bullet Jumps
   1. 6 shots at 0.050”
   1. 6 shots at 0.055”
   1. 6 shots at 0.060”
3. Group #3: 0.075-0.085” Bullet Jumps
   1. 6 shots at 0.075”
   1. 6 shots at 0.080”
   1. 6 shots at 0.085”

Of course, if you’re current load uses a 0.010” jump, you could change Group #1 to be 0.005-0.015” or 0.010-0.020” to test how “durable” or consistent your current load is a 0.010” range of bullet jumps that you will likely experience, if you don’t adjust seating depth every 100 rounds or less.

Within each group, Mark fires the shots round-robin style. For example, in Group #1, they’d fire one shot with a 0.015” jump, then one shot with a 0.020” jump, then one shot at 0.025” – then they’d repeat until all 6 shots are fired at each bullet jump. Then they’d clean the barrel, foul the bore with a couple of shots, and repeat the tests for Group #2, and so on.

Two important notes before you do this:

1. You must carefully measure the distance to the lands on your barrel with an accurate and repeatable method. How most shooters do that is not precise enough to be within +/- 0.010” – I know that was true for me. Click here to learn about the only two methods I know of that are repeatable to +/- 0.002” or less. If you don’t do this, you likely won’t be testing what you think you are.
2. Adjusting your seating depth will affect your chamber pressure, so, as always, you should be careful when changing a load and watch for signs of excessive pressure. The Sierra Reloading Manual says that adjusting seating depth to match your rifle’s throat/freebore and maximize accuracy “is fine, but bear in mind that deeper seating reduces the capacity of the case, which in turn raises pressures. Going the other way, seating a bullet out to the point that it actually jams into the rifling will also raise pressures.”

Results from A Few 18-Shot Challenges
We wanted to share a few of the results from these types of challenges that Mark has already collected using his electronic target system at 600 yards.

6×47 Lapua with Berger 105 Hybrid
Below are the 3 targets from this challenge with an 18-shot group on each one. I added a callout beneath each target for the vertical extreme spread that was measured for each group by the electronic target system at 600 yards (also highlighted in the yellow box on the readout).


The Problem with Extreme Spread
While measuring the extreme spread of a group is very easy to do and useful, one of the problems of only looking at extreme spread of the group is that it really only takes two shots into consideration – namely the two that are furthest apart. Where the other 16 shots hit in no way affects the extreme spread, which means we’re ignoring 88% of the shots fired! For example, if you look at the target above on the left you can see shots are evenly distributed vertically. However, the target in the middle has most shots in a narrow vertical window, except for one outlier, namely shot #1. In fact, if you excluded shot #1 from the middle target the extreme spread would drop from 3.9” to just 2.1”. Now cherry-picking data to exclude is the exact opposite of good science, so I’m certainly not suggesting we do that. But it goes to show how drastically an extreme spread can change based on the placement of a single shot. It simply doesn’t take advantage of the full sample size.

Bryan Litz discussed this topic at length in Modern Advancements for Long Range Shooting Volume II. Bryan carefully explains this in Chapter 1 of that book, but here an excerpt with his recommendation:

“Measuring the extreme spread of shot groups is quick and easy, but it’s not actually a very good measure of dispersion. What do I mean by a good measure? A good measure should give you useful information, which is information you can use to make good decisions. When you look at the extreme spread of a 5-shot group, that measurement is determined by only 2 out of the 5 shots. In other words, only 40% of the shots are considered in the measurement. Even worse, for a 10-shot group, a center-to-center measurement is only using information from 20% of the total shots. Since the extreme spread, center-to-center measurement, is determined by only a small portion of the total shots available, it’s just sort of an indicator of precision. There are many alternative measures of precision. You could measure the location of each shot and calculate vertical and horizontal standard deviation (SD), radial standard deviation (RSD), circular error probable (CEP), etc. You could get really carried away with statistical methods of characterizing precision. Taking a step back and considering options for measuring dispersion; we want something more descriptive than extreme spread, but don’t want to go crazy with statistics. It’s my opinion that the mean radius of a shot group is a well-suited measurement for this task. Mean radius, also known as average to center is self-explanatory; it’s the average distance from each shot to the center of the group.” – Bryan Litz

 

[Get Off My Lawn]

Average distance to center (ATC) takes all the shots into consideration, and therefore is more representative of the entire group and not simply the two shots that fell furthest apart. It’s not that extreme spread isn’t useful. There are shortcomings to ATC as well. You could have two groups with the same ATC, but one has most shots tight and one flier way out of the group and the other group is more well-rounded without a flyer, but the primary shot cluster is slightly larger. In this case, the ATC was identical, but the ES was different. So, I’m certainly not claiming ES is irrelevant or not useful. While ATC does include all shots fired in the calculation, maybe we should analyze both ATC and ES when looking at groups to keep a balanced perspective.

ATC is more difficult to measure and calculate by hand, but software like the OnTarget Shooting app can analyze your target and provide ATC and ES for you, along with other stats.

The chart below shows the equivalent data for vertical extreme spread taken from the targets above and converted to Minute of Angle (MOA), instead of inches at 600 yards. It also shows the average distance to center (ATC) that Bryan suggested as a more complete or representative measure of the dispersion of a group.

You can see 0.050-0.060” bullet jumps resulted in the smallest extreme spread. In fact, the ES for the shorter jump (0.015-0.025”) turned out to be 48% larger, and the average distance to center between those is 100% larger! The 0.050-0.060” bullet jumps clearly produced the most consistent vertical at long range in this test.

6BRA with Berger 105 Hybrid
Mark also ran this test with a rifle chambered in 6mm BR Ackley Improved (a.k.a. 6BRA) firing Berger 105 gr. Hybrid bullets at the same jump ranges: 0.015-0.025, 0.050-0.060, and 0.075-0.085. Let’s take a look at those results:

You can see the group with the largest jump (0.075-0.085”) produced the smallest extreme spread. The shortest jump had the largest ES at 0.84 MOA, which is 47% larger than the 0.57 MOA ES achieved with the 0.075-0.085” jumps. When it comes to ATC, all three groups were very similar. If the ATC is similar but the ES is not that means there must have been a few significant fliers in the shorter jumps, but the other shots must have clustered reasonably close together to still achieve a low ATC. On the other hand, the lower ES of the farthest jumps means it didn’t have fliers as significant, but the main cluster must have been slightly larger for the ATC to end up the same. Overall, the load with the 0.075-0.085” seems to be the best overall performer for this rifle.

6×47 Lapua with Berger 115 DTAC
Finally, Mark did a similar 18-shot challenge at 3 different bullet jump ranges with David Tubb’s 115 gr. DTAC RBT Closed Nose bullet. For the middle range on this challenge, Mark chose to test 0.030-0.040” instead of 0.050-0.060” that was used on the prior two tests. Here are the results:

On this one, it looks like the shortest jump actually had the smallest extreme spread – although it was only by 0.01 MOA! Obviously that middle bullet jump range of 0.030-0.040” had a very similar extreme spread, but it also had the lowest ATC of any of the groups. So, if I were trying to pick between these jumps, I’d go with the middle group because the ATC is 13% smaller than the 0.015-0.025” results, even though the ES is 2% bigger. Once again, the Average Distance To Center (ATC) takes all 18 shots into consideration, while the Extreme Spread (ES) only takes 2 of the 18 shots into consideration when doing the calculation. So, if you’re going to weight one metric more than the other, I’d suggest ATC.

I do have to wonder if this test for the 115 gr. DTAC would have favored a 0.040-0.050” jump range, if they’d have tried that for the middle range. I went back to the bullet jump research data for the 115 DTAC, and the chart below shows where the sweet spots were over the 6 rifles Mark collected data over:

You can see that 0.030-0.040” had an average vertical spread of 0.62 MOA over the 6 rifles that are represented in the data above, which is EXACTLY the same as the results in this 18-shot challenge. Isn’t that crazy?! The average over the 18 shots fired here with one rifle and the average over the 6 rifles tested with 3 shots in that range each, which we covered in the previous post, both ended up being EXACTLY 0.62 MOA! While the fact that they are identical to the hundredths place is likely a coincidence, it gives me a little more confidence in the how repeatable and reliable this data is. You can see above that it was 0.040-0.050” that produced the smallest vertical ES at just 0.31 MOA at 600 yards. I wonder if that would have ended up being the winner if they’d done an 18-shot challenge for that range of jumps instead. Of course, they may not have had all that data when they originally did this 18-shot challenge, since this testing has been a progressive thing over more than two years. If I were using 115 DTAC’s, I might try out that 0.040-0.050” range of bullet jumps.

The Challenge & Up Next
If you’re one of those guys who already has a great load, but it uses 0.020” of jump or less, Mark wants to challenge you to go run this test for yourself. After 54 rounds, he bets you might find something that works better than what you’ve been using. That has been the case each time he’s ran through these tests with other shooters! With COVID-19 stay-at-home orders in most places and rifle matches canceled, maybe it is a good time to try to tune on your load to be ready when things start back up!

Up next, I’ll wrap up this whole series and offer a few suggestions on how to integrate bullet jump into your load development process. While the 18-shot challenge is a good way to test a couple of further bullet jumps against your current load, what is the best way to go about this to develop a load from scratch? If we now have another variable we need to tune in load development, how do I find a good load without having to shoot 100+ rounds doing load development? Do I have to test every 0.005” to find the best bullet jump? What order should I do this in, powder charge or bullet jump first? Great questions! In the next post, I’ll share some personal suggestions and advice from other top shooters in the next post to try to help you get to a good load in the fewest rounds possible.

 

[Get Off My Lawn]

Another post of this series came out today, links to all of them are at the bottom of this post.
https://precisionrifleblog.com/2020/04/28/bullet-jump-research-and-load-development-tips/
Bullet Jump Research: Executive Summary & Load Development Tips
This is the last post in a series of articles focused on bullet jump research that has been conducted more than two years by Mark Gordon of Short Action Customs (Who is Mark Gordon?). In this post, I’ll provide an executive summary of what we covered and provide a few tips for how to apply this new knowledge in our load development.

The first article provided a comprehensive overview of what 10+ of the most respected books and reloading manuals had to see about bullet jump and laid the foundation of what bullet jump is, along with other concepts like freebore, lands, seating depth, etc. Everyone from accomplished scientific researchers to world-champion shooters suggested either seating bullets into the lands or minimizing jump to within 0.020” of the lands or less for the best precision. Benchrest World Champions and other experts explained that when seating bullets close to the lands, changing bullet jump by 0.002-0.005 inches can potentially have a dramatic affect precision.

Then we looked at How Fast Does A Barrel Erode?, which focused on how quickly the lands of a rifle barrel usually erode for popular mid-sized cartridges used in precision rifle matches, like the 6mm Creedmoor, 6 Dasher, or 6.5×47 Lapua. There we saw it is common for that lands of a barrel to erode by 0.004-0.007” every 100 rounds.

That means if we’re in a major PRS/NRL match where you fire 200 rounds over two days, by the last stage our bullet jump will be 0.008-0.014” more than it was on the first stage! So, if the experts are saying that changing bullet jump by just 0.002-0.005” can have a “dramatic” impact on precision, what will 2-7 times that much do?

It seems we usually apply best practices that were established in other shooting disciplines, but if we’ll be in precision rifle matches that require 100-200 rounds, maybe our priorities should be different. In other types of competitions, like Benchrest, shooters may literally load their ammo at the range as they’re shooting. Extreme Long Range (ELR) has much lower round count. F-Class and other competitions allow sighters, so if your vertical shifted you just adjust a click or two to center your group before you fire your shots for record. However, in PRS/NRL matches first round hits matter, round counts are high, and we don’t get to fire sighters or recheck our zero.

What if instead of looking for the one exact bullet jump that provides 100% optimal precision and having to constantly adjust the seating depth as the lands of the barrel erodes, we instead looked for the bullet jump that is very forgiving AND still provided good precision over a wider range of jumps?

Now let’s think about the guys who aren’t reloading: If a shooter plans to simply shoot match-grade factory ammo, could we optimize the freebore of the chamber to be a bullet jump that would continue to provide good precision over a longer period of time as the barrel wore? I recently measured 400 rounds of various match-grade factory ammo (for an upcoming test), and it’s not uncommon for the length from the base of the case to the ogive of the bullet to vary by 0.008” or more even in within the same box of “match-grade” ammo. So, it seems like those guys using factory ammo might have similar priorities.

What if absolute peak precision might not be the only priority we are trying to balance? I totally understand that in some shooting disciplines, like Benchrest, optimal precision is the absolute highest priority and nothing else is even a close second. But what if we came at this from a different angle and tried to see if there was a way to balance priorities of both precision and a forgiving bullet jump?

That line of thinking is what led Mark Gordon to start testing bullet jump. Mark builds custom precision rifles at Short Action Customs and he brings an obsessive approach to optimizing every facet of the rifle system. His methodical and analytical approach eventually led to research on the ammo his rifles were being fed. It is important to understand Mark didn’t start this research with a theory to prove. He simply wanted to know if there were any small improvements he could make to the chambers on his rifles to improve their performance over his competition. Was there something that seemed to work well across a wide range rifles? Mark started experimenting bullet jumps and collecting data over two years ago, and some of his results seem to challenge conventional wisdom.

Mark used an approach similar to the Audette Ladder Test and OCW method, but the goal was to not find the most forgiving powder charge weight, but the most forgiving bullet jump. He wasn’t looking for the specific bullet jump that grouped the best, but the largest window of bullet jumps that provided a similar point of impact. That means the rifle would be more consistent from the start of the match to the end of it or could shoot a particular kind of match-grade factory ammo really well for a longer period of time.


Here is how Mark performed what he calls the 20-shot jump test:

1. Carefully measure the bullet seating depth required for the bullet to very lightly contact the lands (i.e. 0.000” jump, but not jammed into the lands). Watch my video showing Mark Gordon’s method on how to do this.
2. Load up 20 identical rounds, except vary the bullet seating depth in 0.005” increments. #1 = 0.000” jump, #2 = 0.005” jump, #3 = 0.010” jump, … , #20 = 0.095” jump.
3. Fire the rounds at 600 yards, recording the point of impact coordinates for each shot with an electronic targeting system and muzzle velocities with a LabRadar.

We then analyzed the vertical dispersion of the data he collected. The goal was to find a range of bullet jumps that all had similar vertical points of impact (POI) at distance. I explained how we took the target data and turned it into the charts in detail in the Bullet Jump: Is Less Always Better? post, and I’d encourage you to go read that if you haven’t already. I won’t be repeating all that here.

 

[Get Off My Lawn]

The Results For Berger 105 Hybrid
Mark has repeated the same 20 shot bullet jump test using the Berger 105gr Hybrid over 10 different rifle/load configurations. That included 5 different 6mm cartridges: 6×47 Lapua, 6mm Creedmoor, 6 Dasher, and 6 BRA. Those rifles also had a variety of actions, stocks, chassis, brands of barrels, contours, and twist rates. (Read more about the rifles tested here.) While there was a lot of variation in the rifles tested, there seemed to be some similarities in terms of performance based on bullet jump.

The chart below graphs the results for all 10 rifle configurations, meaning it represents data points for 200 shots fired with the Berger 105 Hybrid bullet. The gray area is widest on the left side of the chart and it narrows as you move to the right, with the tightest area around 0.070 to 0.080” of bullet jump. That means over all 10 rifle/load configurations, the vertical extreme spreads appear to be the tightest at 0.070 to 0.080” of bullet jump.

Another interesting thing about the chart above is it appears to be saying that when you have minimal bullet jump (0.000-0.010), that is where it appears to be least forgiving in terms of changes in bullet jump. You can tell that by the widest area of gray on the left of the chart. That means if you start off with 0.000” of bullet jump, after you’ve fired 100 rounds and the throat eroded by 0.005”, and therefore you’re jumping 0.005”, you may very likely experience some vertical stringing, and in some cases it looks significant (over 1 MOA).

We also looked at what the average vertical extreme spread was over two ranges of bullet jumps:

• 0.010” wide range of bullet jumps: What you might expect the lands to erode over 150-250 rounds with popular precision rifle cartridges
• 0.020” wide range of bullet jumps: What you might expect the lands to erode over 300-500

We looked at the results for the Berger 105 Hybrid Bullets in detail (view here), but we also published research data Mark collected across 9 different rifles/load configurations using Hornady’s 6.5mm 147 gr. ELD-M bullet, and data over 6 rifles using David Tubb’s 115 gr. DTAC RBT bullet (view detailed results for those 2 bullets).

Below are summaries of the average vertical extreme spread over all 3 bullets for both a 0.010” wide window of jumps, as well as the 0.020” wide window of jumps. These two charts basically summarize all the research data presented over the last two posts, and allow you to see the trends of the bullets side-by-side. In this visual, the lower the line the better, because that indicates a smaller extreme spread.

While there are slightly different patterns between each of the bullets, it does appear none of the bullets have the most forgiving bullet jump under 0.030”. The most consistent vertical POI over a wide range of bullet jumps appears to be at 0.040” or more bullet jump. Jumps that have traditionally been considered absurdly long, like 0.080” or more, actually seem to produce less vertical shift in POI as the barrel wears than when the bullet is seated near the lands.

So What Does All This Mean?
Remember, Mark wasn’t looking for the specific bullet jump that grouped the best, but the largest window of bullet jumps that provided a similar point of impact.

This research is NOT claiming you can’t get extremely precise groups seated close to the lands or even into them. Of course, you can! However, what the data does appear to indicate is that if you are seating bullets 0.030” or less from the lands, you could experience a vertical shift in point of impact if you don’t tightly manage your seating depth and adjust it regularly (e.g. every 100-200 rounds). While minimal jump may produce smaller groups than if you were jumping 0.060” or more, that isn’t necessarily a hard and fast rule either.

Here is the question we were original hoping to answer: What if instead of looking for the one exact bullet jump that provides 100% optimal precision and having to constantly adjust the seating depth as the lands of the barrel erodes, we instead looked for the bullet jump that is very forgiving AND still provided good precision over a wider range of jumps? This research seems to make a strong case that the answer to that is found at longer bullet jumps. However, the specific “sweet spot” seems to vary based on the specific type of bullet you are using.

I created the illustration below to try to help people understand this concept. I admit this is likely grossly over-simplified, but it seems helpful. The green dots are intended to represent a group at some point in time, and the red dots are another group fired after the lands eroded 0.010” over 150-250 rounds fired.

The example above literally came from the test results for 115 DTAC. The 0.8 MOA Extreme Spread shown on the left is what was measured on average over 6 different rifles when the bullet jump was changed from 0.025” to 0.035”. The 0.3 MOA shift on the right is what the ES was for bullet jumps from 0.075” to 0.085”. Now, that does not mean the size of the groups reflects what happened, because we didn’t test group size at each specific jump.

The truth is, we could easily miss large patterns like this which occur over round counts of 100 or more. While we may fire a couple of groups in a row, we don’t do that over 100-200 rounds in a row. If you are shooting precision rifle matches where there aren’t sighters, round count is high, you can’t recheck your zero, and you’re trying to make first round hits on small targets at long range … this seems like relevant and actionable insight!

Support From A Statistician, Top-Rank Shooters & Industry Pros
As Mark began sharing this with friends in the shooting industry, he quickly met some skepticism on whether the data he collected was reliable or simply random patterns. Mark also wanted to know how much confidence he should have in the results, so he enlisted professional help in reviewing, analyzing, and processing the data. Earlier this year, a statistician named Walter Meyer analyzed all of the raw data, and he concluded that the findings showed a “strong statistical improvement in the bullets ability to hold tight vertical at distance” and “statistically significant conclusions are appropriate.” He calculated p-values less than 0.05 with two different approaches, meaning there is strong evidence that the patterns aren’t random. Walter was careful to add, “Extrapolations to other tests, bullet type and environmental conditions must be made with caution by the subject matter expert.” That means we shouldn’t assume the results for a particular bullet represent how other bullets might behave, which is an important point.

As I shared in the first post with results, after Mark started sharing his finding with a couple of the top-ranked PRS/NRL shooters, they tried this for themselves and are now believers. One of those is Scott Satterlee, who has placed in the top 10 in both the PRS and NRL in the overall national standings in recent years and is clearly one of the best shooters in the country. Over the past two years, Scott has experimented with freebore and bullet jumps all the way out to 0.250 inches! He is now on his 5th barrel since he’s been experimenting with longer bullet jumps and said, “This isn’t something that I’m still wondering if it’s true or not. After 5 barrels, I know it’s real. There is a real improvement and benefit here.”

 

[Get Off My Lawn]

Even more recently, a friend in the industry reached out to me after reading my articles on this research to let me know it aligned with some extremely in-depth research they’ve conducted. Scott Seigmund is Vice President of Accuracy International of North America, and here is what he shared with me:

“A few years ago, we did extensive data analysis on 338 rifle test groups involving two significantly different freebore lengths. The test involved 25 different rifles (50 in total). One group of 25 rifles had a standard CIP 338 Lapua chamber while the second group of rifles had chambers with a large increase in freebore. The data was analyzed by David O’Reilly, our operations manager and statistical expert. The results even surprised me with an increase in accuracy of 19% with the 300 grain bullets jumping about 0.100″. The test was done using the same lot of 338 Lapua 300 grain Scenar ammunition and over 2500 shots collected. While I would love to claim credit for this “discovery” it was basically gifted to us by Wade Stuteville. Wade was on to this bullet jump thing a long time ago and has done a lot of testing in this area. He’s one of the most intelligent people I know and has no ego about what he knows. Just a great, caring, and giving person.” – Scott Seigmund

Wow! The test involved 50 rifles and over 2500 shots! That sounds like some serious research, and I’d think those results are conclusive. Thank you, Scott, for your willingness to share that with the rest of us!

In further conversations, Scott said as they’ve also done considerable research on the 300 Norma Mag as they were prepared to submit their rifle for the SOCOM Advanced Sniper Rifle contract, and they found longer bullet jumps improved performance on that cartridge also.

Over the past few months, I’ve had a ton of conversations with industry pros about bullet jump, and multiple people have brought up Wade Stuteville as someone who had originally told them about the performance you can potentially get at longer jumps. Wade is a veteran shooter who was the PRS Overall Champion several years ago, and he is also one of the most respected gunsmiths in the country (read more about Wade). I’ve known Wade for several years, so after hearing his name come up so many times, I gave him a call to get his perspective.

“From what I’ve seen the big, magnum cartridges all like to have longer jumps. But, even our match cartridges (like the Creedmoors, x47 Lapuas, BR’s, Dashers) have that spot around 0.010-0.020” bullet jump where they shoot good, but usually there is another spot way back that is much wider and more forgiving. A lot of bullets don’t seem to shoot as good in that 0.020-0.050” range, but then come back into a place around 0.050+ inches where you might be able to move the jump from 0.050 to 0.100” and it shoots good everywhere.” – Wade Stuteville

Wade went on to say that when the Berger 105 Hybrid bullets first came out, he started shooting them from a 6×47 Lapua and was getting great performance seating them close to the rifling, and he’d consistently keep them tuned with very minimal jump. After a match he’d clean his gun, remeasure the distance to the lands, and then take any ammo he had left over from the match and bump his bullet out to the new seating depth to keep them close to the rifling. Wade went on to say that he first discovered the longer bullet jumps on accident. He had two 6×47 rifles that were basically identical except one had more rounds on it than the other. One day he shot the ammo that had been tuned for the chamber with less rounds on it in the other rifle, which meant it was jumping much longer – and it performed as well as anything he had shot! Wade said that is what triggered him starting to experiment with jump. He discovered on his 6×47 rifles he could start off jumping the 105 Hybrid’s around 0.080” and never have to change the seating depth over the entire life of the barrel and it’d perform great the whole time. Wade explained, “Over the life of the barrel, my jump might change from 0.080” to 0.130” or something, but it never really comes out of tune. And I’ve had a lot of cartridges that have been that way in the past.”

While much of this seems to be counter to “conventional wisdom” (which I outlined in the first post), there sure seems to be some pretty compelling evidence from this research and the experience of other respected sources in the industry.

Load Development Tips
I originally planned to make a recommendation for how to integrate bullet jump into your load development. However, I’m still experimenting with the best way to do that myself. So instead of prescribing how to go about it I will simply offer a few tips based on this research data and share suggestions from others in the industry. Armed with that information, you can make an informed decision on how you might try this out for yourself in your load development. Also, if you have a good way you test jump during load development, please share that with the rest of us in the comments!

Important: Adjusting seating depth to match your rifle’s throat/freebore and maximize accuracy “is fine, but bear in mind that deeper seating reduces the capacity of the case, which in turn raises pressures. Going the other way, seating a bullet out to the point that it actually jams into the rifling will also raise pressures.” – Sierra Reloading Manual

Measure Your Distance to The Lands With A Precise Method
Until a few months ago, I was measuring the distance to the lands like most people do. I thought it was accurate, but I was off by almost 0.100” in some cases! No joke. It turns out you can seat a bullet well into the lands without it leaving marks on the bullet or getting stuck in the rifling. Measuring the distance to the lands in a way that is accurate and repeatable is harder than it seems. There are only two methods I know of that allow you to measure the distance in a way that is repeatable within +/- 0.002”; Mark Gordon came up with one and Alex Wheeler teaches another. You can learn more about both on this page: How To Measure The Distance To The Lands On Your Rifle Barrel.

If you take just one piece of advice from all this, I might suggest it be to try this measurement method. I bet the results surprise you. Honestly, if you are not measuring the distance to the lands with one of these methods, I bet you aren’t testing what you think you are.

Measuring CBTO vs COAL
If you are concerned with bullet jump, you need to measure from the base of the cartridge to the bearing surface of the bullet (i.e. CBTO or Cartridge Base To Ogive), not from the base to the tip of the bullet (i.e. COAL or Cartridge Overall Length). Even if bullet tips were completely uniform (and they never are), remember that bullet jump is the distance a bullet travels before it’s bearing surface touches the rifling in the barrel – so measuring CBTO (Cartridge Base To Ogive) is a much better way to ensure that jump is uniform. (Read more: Article from Bryan Litz on CBTO vs. COAL)

To measure this, you need a caliber-specific bullet comparator. I use one from Hornady, and you can get it in a kit with 14 caliber inserts that covers all major calibers on Amazon.

Establish Seating Depth, Then Powder Charge
Mark tested 3 different loads for the 6.5mm Hornady 147 gr. ELD-M from the same rifle, and all of them resulted in a very similar “sweet spot.” Regardless of the shooter, order the shots were fired in, or amount of powder used, the data showed a sweet spot around 0.060” of bullet jump each time the test was run (read more here).

Alex Wheeler, owner of Wheeler Accuracy and a respected gunsmith who has built some of the best shooting 1000 yard Benchrest and F-Class rifles, seems to agree with this idea:

“From my experience powder charge will not drastically affect the correct seating depth. Meaning if you change your powder charge the gun will not go from preferring a .010 jump to a .060 jump. It may move a few thousandths, but I think you can use any powder charge you want to rough in on seating depth.” – Alex Wheeler

After doing more than 2 years of research on bullet jump, Mark Gordon believes bullet jump is a more course adjustment to a load than powder charge, meaning a small tweak to bullet jump can often has a larger impact on performance than a small tweak to powder weight. I remember where I was when I first heard Mark propose that, because it was so foreign to my way of thinking. I’d been approaching it from the other direction completely. However, I can’t say that doesn’t fit my experience, and if that is the case then it makes sense to start with the most course adjustment before we move to further steps to refine a load.

 

[Get Off My Lawn]

Scott Satterlee explains that when he does load development, he starts with the same powder charge weight that worked best in his last barrel or if he’s working up a load from scratch he’ll simply start with a powder charge he knows is safe. Then here is his two-step load development process.

1. Bullet Jump for Group Size/Shape: Scott tests various bullet jumps to find the one that produces the smallest vertical extreme spread at long range. He prefers to tune a load at either 800 or 1000 yards. In this step, he is 100% focused on group size and shape. He is not just looking for a small group, but the shape is important too. Scott believes a group in the shape of a triangle is great, and one that looks like the 5 on dice is outstanding. He does not like to see a group that is short and wide, even if the spread is tiny. Scott said from his experiencing, following a group like that leads to the road of destruction, because it is deceptive and won’t be a consistent performer long-term like a group in those other shapes. Scott explains that what you’re looking for is not just a small group, but an even distribution in the shots within the group. From a statistical perspective, I think Scott is saying that you want a very small Average Distance To Center (ATC), which is also sometimes called mean radius. That doesn’t mean you can ignore the extreme spread, but he doesn’t simply pick the group with the smallest extreme spread. (I’ll touch more on the specific jumps Scott tests in the next section below.)
2. Powder Charge for Lowest Velocity Extreme Spread: Once Scott has found the optimal bullet jump, he starts varying the powder charge with the goal of finding the lowest extreme spread (ES) in muzzle velocity. In this step, Scott isn’t looking at group size and even said he might just fire the bullets into a berm, because he is 100% focused on finding consistent muzzle velocities. While many shooters reference the muzzle velocity standard deviation (SD), Scott prefers to use ES as his guiding metric. He says occasionally you’ll have one shot out of a long string be very different, and SD glosses over that anomaly more than ES does, but that kind of thing could result in a miss in a match.

For more details on Scott’s approach to load development, I HIGHLY recommend listening to a recent podcast where he shares all the details. It is VERY interesting! Modern Day Sniper Podcast: Scott Satterlee & Handloading. The podcast is hosted by Phil Velayo and Caylen Wojcik, who are top-ranked precision rifle shooters and they know what they’re talking about. At SHOT Show earlier this year, Scott Satterlee, Mark Gordon and I had a long conversation, and this podcast is very similar to listening in on our conversation at SHOT. Scott has an unorthodox/pragmatic approach to load development, which I won’t attempt to repeat here. I promise it will challenge how you think about this stuff and I bet you walk away with at least one or two good ideas for how you could improve your own approach.

What Jumps to Test
Let’s first look at the data from Mark’s bullet jump research. Below is a little different view into the same data we’ve looked at over the last two posts, which helps visualize where the “sweet spots” are for the three bullets Mark has compiled considerable data for:

You can see all of the bullet jumps that produced consistent vertical POI at long range were at least 0.040” from the lands or more. Most of the time it was actually 0.050″, which is also what Wade Stuteville said his experience was. Remember, this isn’t saying you can’t get tiny groups at shorter bullet jumps, but the data is simply showing that shorter jumps are less tolerant of changes in bullet jump. At least for these three bullets, jumps under about 0.040-0.050” are not as forgiving and consistent as the distance to the lands changes.

So if finding a forgiving bullet jump is a priority for you, the data seems to be suggesting you start testing around 0.040” and go out from there. While Mark’s testing was limited to bullet jumps out to 0.095”, Scott Satterlee has experimented with bullet jumps out to 0.250” on his 6mm Creedmoor – and Wade Stuteville said he’d also tested cartridges out 1/4 of an inch and even some closer to 3/8 of an inch (0.375″)! However, while this may change slightly barrel to barrel, most recently Scott has been jumping around 0.120”.

While you might find good precision beyond 0.120”, longer jumps may require additional chamber freebore, meaning a gunsmith needs to modify your chamber to be able to jump that far. With traditional chambers, jumping 0.120” or more may require you to seat the bullet too far in the case. Scott says that he never wants the bearing surface of the bullet to be below the neck/shoulder junction on the case. That helps you stay away from the base of the neck where the “dreaded donut” could lead to shot-to-shot inconsistencies (more on the donut). Also, seating bullets further out allows more volume in the case which can actually allow you to achieve faster muzzle velocities without increasing pressure. (Read Bryan Litz explaining more about this.)

Scott Satterlee says when he is testing jump, he doesn’t do anything too drastically different than what the Berger Bullets Reloading Manual recommends (read that here), except he usually tests with jumps at 0.030”, 0.050”, 0.080”, 0.100” and 0.120”, rather than the intervals Berger suggests. Scott said sometimes he may just start at 0.050″. After he figured out which one groups best (as explained in the prior section), he then tests jumps a little below that and maybe 0.010-0.020” above it to make sure it continues to group well. That is how he makes sure that is a “durable” jump.

By the way, I do want to point out that Berger Bullets is the only reloading manual or published book I’ve found that actually recommends testing bullet jumps out to 0.100” off the lands or more. As we saw in the first article in this series, virtually everyone recommends jumping 0.020” or less for the best precision. Berger is the one outlier I’ve come across, but this research seems to confirm that they have been giving us good advice. Thanks, Berger!

I’ll try to side-step the debate of how many rounds you need to fire at each bullet jump for your results to be “conclusive” from a statistical perspective. There has been a lot of debate on that topic in the comments of this series of posts. There seems to be a purist/mathematical view which leads to very large sample sizes, and a practical/pragmatic view that says you can do it with one 5 shot group. I’ll leave it up to you guys to decide where you fall. Simply put, the larger the sample size the more confidence you can have in the results.

Alternatively, you could do load development in a similar fashion to Mark’s 20-shot jump test, testing from touching the lands out to 0.095” or even 0.120”. However, the statistician Mark had analyze the data did say that testing in 0.005” increments didn’t seem necessary from a statistical perspective, although having data in 0.005” increments helped as he did calculations for p-tests to ensure these results were statistically significant. His professional opinion was that tests in 0.010” increments would have reached the same conclusions.

If you do want to use something more like Mark’s 20-shot jump test, you might consider running through it at least 3 times to confirm the patterns you are seeing persist. To conserve barrel life, you might consider starting at 0.040” or 0.050″ from the lands and test in 0.010” increments, as the statistician suggested. If you did those things you could test the following 9 jumps with 3 to 5 shots each, and then graph the vertical POI of your results and look for the flat spots: 0.040, 0.050, 0.060, 0.070, 0.080, 0.090, 0.100, 0.110, 0.120. For more details on Mark’s approach and what I mean by “flat spots,” read this post.

 

[Get Off My Lawn]

Adjust Your Parallax!
My last tip is when we’re doing these kinds of tests and making decisions based on relatively minor differences in group size or patterns in shot-to-shot POI, it is especially critical to ensure your parallax is adjusted properly. Even at 100 yards, you can have shot-to-shot variance from parallax, which just adds noise to your data and can result in false positives and bad decisions. Not sure how to adjust your parallax? Watch this video

Shortcuts To Loads & Components
While some people love to tinker with load development, there are others that simply want to find a load in the shortest number of steps possible. For the latter group, I want to mention a couple of resources that could be potential shortcuts for finding a good powder charge or combination of components to use.

• What The Pros Use: Load Data. This series of articles shows what components and specific powder weights the top-ranked precision rifle competitors in the country are running in their match ammo.
• My Complete Load Data: This is the page I use to keep track of all my load data, for cartridges like 6mm Creedmoor, 6XC, 6.5 Creedmoor, 7mm Rem Mag, 300 Norma Mag, 338 Lapua Mag, 375 CheyTac, and more. It is actually what I use to reference my own load data, so it’s always kept up-to-date.

The Point of Diminishing Returns: How Much Does It Matter?
Finally, there are a couple timely reminders we should keep in mind. If you enjoy tinkering, then I don’t want to pour cold water on you. But there is definitely a point of diminishing returns when it comes to load development. For example, reducing your group size from 0.5 MOA to 0.1 MOA may only increase your hit probability at long range by 1-2%. That isn’t just my opinion, but is based on hard data you can see on the chart below and read more about here: How Much Does Group Size Matter?

Shrinking your muzzle velocity’s standard deviation from 10 fps to 3 fps may only increase your hit probability at long range by 1-2%. You can see that in the chart below and read more about that here: How Much Does SD Matter?

As always, it depends on the size of the target and other factors. However, if you aren’t shooting extremely tiny targets or Extreme Long Range (ELR), and you aren’t competing at the absolute highest levels (i.e. you aren’t one of the top 25 shooters in the country) – tuning your load to the Nth degree may not matter as much as you think. Hopefully, those stats help us put into context that point of diminishing returns.

I wrote an entire series of articles called “How Much Does It Matter?” that took an objective approach to those factors, as well as many others. If you have not ever read that, I would highly recommend it! I promise you’ll learn something, and probably find a few surprises. I know I did!

Series Wrap-Up!
I hope you guys enjoyed this series of articles on bullet jump as much as I did! I know it challenged a lot of things I had simply been assuming were the unquestionable truth in the past. Even if you’re a still a skeptic, I’d challenge you to go try it for themselves. That is exactly what I plan to do!

And to Mark Gordon – Thank you for being willing to share your hard work with the rest of us! I know you could have kept all this data private and thought of it as a competitive advantage for Short Action Customs, but we appreciate your openness. We all got to learn something from it, and this is a huge contribution to the shooting community! It also clearly shows the methodical approach and extreme lengths you go to at SAC to ensure the rifles and products you make are performing at the highest levels. Lots of people think about doing stuff like this, but very, very few execute on that and see it all the way through. Thank you for your passion and extreme internal drive for excellence!

I’ll end with this quote, which seems fitting for this topic and Mark’s research:

“It is easy to sit about the fireside or under the shade of the home trees, after a day’s work at competitive rifle practice, and talk over the causes of bad shots, and it’s good fellowship’s pleasures are not to be denied; but it’s not so easy to prove by repeated and, maybe, costly experiments that our fine theories are correct”. – Franklin Mann, The Bullet’s Flight From Powder To Target (Published 1909)

Here are links to all the articles in this series:

1. Bullet Jump & Seating Depth: Best Practices & Conventional Wisdom
2. How Fast Does A Barrel Erode?
3. Bullet Jump: Is Less Always Better?
4. More Bullet Jump Research!
5. Mark’s 18-Shot Bullet Jump Challenge!
6. Bullet Jump Research: Executive Summary & Load Development Tips

 

[Sasquatch]

This series of articles has confounded me because it really seems a black art to get the right jump. I can't see any science behind it the way I do by powder selection/weight, etc. Not just because of this article, but I no longer try to get max length (mag) out of my rounds- because it has caused more problems like getting bullets stuck in the lands.

I can't follow this 'try different jumps' method, because I think the effect on volume of the case has a bigger impact than the jump to the lands- any tweaking of the jump means I would _also_ have to tweak the powder/charge to compensate. Not a good exercise to change two variables at once. If I seat a bullet deeper in the case, I've decreased case volume, increased pressure and burn rate, etc. So just getting lucky by trying different jumps which I happen to hit a node is ineffecient.

I've started playing with GRT, which does powder burn calculations and timings of when the bullet leaves the barrel that seems very scientific and repeatable.

 

[REELDOC]

I agree with Sas on changing two variables at one time. Lord knows I'm not as good at the reloading arts as those who wrote the article but common sense change only one variable at a time. I'm a lot less anal than I was when I started reloading but now I develop three pretty basic off the shelf loads with three different powders for each rifle. I start at 20 thou off the lands understanding that even ogives can be +/- a couple thou. I pick the best of the three and tinker with it before I move on to the other two loads. I like to have three loads with three different powders that will hit relatively close to each other whether the accuracy is the same or not.

When mag length becomes involved now you have separate issues to deal with especially when you've got chambers you can throw a cat into.

 

[HTSmith]

Many thanks to Pink Vapor. Very comprehensive and well written.

 

[Get Off My Lawn]

Many thanks to Pink Vapor. Very comprehensive and well written.

Thanks, I only shared their info. None of it was my work.

 

[HTSmith]

It was still a lot of work to put it all together. Now if I could just get enough primers and powder to start testing.