What is causing this group pattern?

Alabamacoastie

Alabamacoastie

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Hi friends. About 8 years ago I built an AR10 from an 80% lower that I drilled out on a CNC machine. After assembling it, I put it in my safe and there it stayed for 8 years. I never even test fired it.

80% DPMS pattern LR308 billet lower made by JL Billet
JD Machine billet upper
Black Hole polygonal 24 inch. 308 barrel
Barrett "look alike" brake
JL Billet 18 inch floating handguard
Rifle length gas tube
JP Industries adjustable gas block
NiB .308 BCG
Magpul PRS gen 1 stock
Standard cheap trigger/ hammer
Cheap Sightmark 8.5-24x50 scope

20190131_141114.jpg

Well today was the day I decided to take it to the range and see if it would shoot. It did! I put about 30 rounds down range, but I noticed an interesting pattern forming on all my targets.

Disclaimer: I spent 4 years on a tactical assault team and 1 year as a shooting instructor. I can tell you all about the fundamentals of breathing, trigger control, blah, blah, blah, and I'm a good shot with every gun I pick up, BUT I have never had any formal training with scopes or long range shooting.

So, after getting my gas block adjusted and getting the scope sighted in, I decided to start shooting groups to see how tight they would be.

I was shooting at 100 yards, from a bench, with the bipod, as pictured above. Wind was calm. About 40 degrees outside. Shooting PMC Bronze .308 rounds in the pic above. Scope was zoomed all the way out to 8.5 magnification which was the lowest setting.

I immediately noticed that my first shot would hit bullseye. 10 seconds later, shot 2 would hit about 2 inches to the right. 10 seconds later, shot 3 would hit bullseye. 10 seconds later, shot 4 would hit 2 inches to the right. I was not moving between shots. I made no scope adjustments between shots. But my rifle produced this same pattern over and over again. One shot on bullseye, next shot to the right, third shot back on bullseye, fourth shot back to the right. Over and over again...

20190131_203902.jpg

Does anyone know why this happened to me over and over again today?

Maybe the scope mount was loose? Maybe the reticle inside the cheap scope is loose? Maybe .308 recoil is too much for the cheap scope? Maybe it's me (but I honestly don't think it's me).

Any opinions would be much appreciated. Especially if you say, "It's not you. It's the scope. Go buy a new scope!"

Thanks everyone!
 
I think @eddie0225 figured it out. We were just talking in chatbox and he mentioned that i need to make sure all of the oil is cleaned out of the barrel before shooting...

After sighting in, I sprayed a bunch of CLP oil directly into the chamber and barrel. That's when my shots started walking back and forth... it had to be all that oil.

What do you guys think about that? Sound feasible?
 
Did you use an inch-pound torque wrench when mounting the scope? If so, did you check the ring/mount manual for the specs? Improper torque, ESPECIALLY too much torque will wreak havoc with your scope's guts.
Is the mount properly torqued? When you mounted, did you cram it as far forward as possible against the lug?
Reticle properly leveled?
Muzzle break locked down and properly timed?
Barrel nut torqued? not likely an issue unless it's actually loose.

Combine all of the with relatively cheap/crap 147gr ammo and a bad trigger.... Get some 165+ match ammo to see for sure what it'll do.

First thing I'd do would be remove the muzzle brake. Take that big heavy thing off is an easy variable to control. Why knows what it's doing to your harmonics, eh? Actually first thing I'd do would be torque specs on all hardware.
 
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I'd blame the scope and the loose nut on the stock second
 
Alabamacoastie said:
Hi friends. About 8 years ago I built an AR10 from an 80% lower that I drilled out on a CNC machine. After assembling it, I put it in my safe and there it stayed for 8 years. I never even test fired it.

80% DPMS pattern LR308 billet lower made by JL Billet
JD Machine billet upper
Black Hole polygonal 24 inch. 308 barrel
Barrett "look alike" brake
JL Billet 18 inch floating handguard
Rifle length gas tube
JP Industries adjustable gas block
NiB .308 BCG
Magpul PRS gen 1 stock
Standard cheap trigger/ hammer
Cheap Sightmark 8.5-24x50 scope

View attachment 102802

Well today was the day I decided to take it to the range and see if it would shoot. It did! I put about 30 rounds down range, but I noticed an interesting pattern forming on all my targets.

Disclaimer: I spent 4 years on a tactical assault team and 1 year as a shooting instructor. I can tell you all about the fundamentals of breathing, trigger control, blah, blah, blah, and I'm a good shot with every gun I pick up, BUT I have never had any formal training with scopes or long range shooting.

So, after getting my gas block adjusted and getting the scope sighted in, I decided to start shooting groups to see how tight they would be.

I was shooting at 100 yards, from a bench, with the bipod, as pictured above. Wind was calm. About 40 degrees outside. Shooting PMC Bronze .308 rounds in the pic above. Scope was zoomed all the way out to 8.5 magnification which was the lowest setting.

I immediately noticed that my first shot would hit bullseye. 10 seconds later, shot 2 would hit about 2 inches to the right. 10 seconds later, shot 3 would hit bullseye. 10 seconds later, shot 4 would hit 2 inches to the right. I was not moving between shots. I made no scope adjustments between shots. But my rifle produced this same pattern over and over again. One shot on bullseye, next shot to the right, third shot back on bullseye, fourth shot back to the right. Over and over again...

View attachment 102806

Does anyone know why this happened to me over and over again today?

Maybe the scope mount was loose? Maybe the reticle inside the cheap scope is loose? Maybe .308 recoil is too much for the cheap scope? Maybe it's me (but I honestly don't think it's me).

Any opinions would be much appreciated. Especially if you say, "It's not you. It's the scope. Go buy a new scope!"

Thanks everyone!
Click to expand...


Alabamacoastie said:
Does anyone know why this happened to me over and over again today?
Click to expand...

I have had the same group results before with one rifle.
The rifle in question grouped very similar to what you're experiencing and my rifle was Very Consistent as well.
If I put enough lead down range it looked like I was running TWO rifles on one target.

After going back through anything that could cause this , dilemma, I discovered the the way the rounds chambered from the magazine up the feed ramp was damaging the projectile.
What I mean by a damaged projectile is it was getting slightly scored, point was slightly deformed as well. I am talking about slight damage, nothing severe enough to make the round not shootable at all.

I removed the firing pin and at various speeds cycled rounds through the rig. At Creep Speed I could see the ( my case the right round - mag fed) round hang ever so slightly and the bullet deformed ~ scored.
The left side feed ramp was fine and the bullet had no where near the damage the right side did.

Why? I attribute the two groups to different aerodynamics between the left & right mag feeds.

Concerning the Sightmark, while they are medium budget optics I believe the Triple-Duty line is stout enough to run on a Semi 308 rig.
I own one or two Triple Duty Sightmarks as well.

Safe Shooting
 
Somethings loose and is moving back and forth between shots. It could be......

The barrel.
The gas block.
The scope or it's mount.
The stock assembly in it's entirety or individual parts.
Bad magazines.
That hideous muzzle brake.

Check 'em all and try again.....
 
YeeHaa said:
I have had the same group results before with one rifle.
The rifle in question grouped very similar to what you're experiencing and my rifle was Very Consistent as well.
If I put enough lead down range it looked like I was running TWO rifles on one target.

After going back through anything that could cause this , dilemma, I discovered the the way the rounds chambered from the magazine up the feed ramp was damaging the projectile.
What I mean by a damaged projectile is it was getting slightly scored, point was slightly deformed as well. I am talking about slight damage, nothing severe enough to make the round not shootable at all.

I removed the firing pin and at various speeds cycled rounds through the rig. At Creep Speed I could see the ( my case the right round - mag fed) round hang ever so slightly and the bullet deformed ~ scored.
The left side feed ramp was fine and the bullet had no where near the damage the right side did.

Why? I attribute the two groups to different aerodynamics between the left & right mag feeds.

Concerning the Sightmark, while they are medium budget optics I believe the Triple-Duty line is stout enough to run on a Semi 308 rig.
I own one or two Triple Duty Sightmarks as well.

Safe Shooting
Click to expand...

This right here makes a ton of sense considering the every other round symptom. I'm thinking that something loose would cause a more erratic symptom affecting every shot differently.
 
I like several of the ideas above, especially the scored bullet left or right feed ramp.
Test each idea individually, without changing anything else, and we will all learn something with your experiment. If you change a lot of things and then shoot the rifle, we will never know.
You can hand feed a few rounds one at a time to test the feed ramp idea.
 
The oil shouldn't cause repeated inconsistent shifts.

I swabbed the bore of my SSG before a class once, as it hadn't been cleaned in forever. I took the first shot at the zero range to ensure the rifle was on, and immediately noticed a 3" high impact over my 100 yard zero. I knew what happened the minute I saw the impact. Higher bore pressure due to the residual oil, despite running a dry patch down it a few times after cleaning.

Unless you're cleaning between each shot, it wouldn't be constantly shifting. Since the pattern is shifting in a pretty consistent pattern, it would seem that something is loose and moving in a rotational manner. Go back and check torque on everything mechanically attached.
 
I'd be highly suspicious of the scope. I had a sight mark way back when and the reticle rotated. They replaced the scope, happened again.
 
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Sounds like you need to polish the feed ramps

:D
 
ok like yee haa was saying, if you want to see if it is the feed ramps and position /side bullet is coming up from load mag up shoot 2 bullets get the said pattern. Pull mag before you shoot third round although its already in the chamber. Once you pulled mag out take out 1 round reinsert mag next 2 shots should be in the same hole or least on the same side of the 2 said sides, that is if that's what's going on if not and shots are still going back and forth it is something else. You could also do like Burt said and polish feed ramps
 
Tim said:
Did you use an inch-pound torque wrench when mounting the scope? If so, did you check the ring/mount manual for the specs? Improper torque, ESPECIALLY too much torque will wreak havoc with your scope's guts.
Is the mount properly torqued? When you mounted, did you cram it as far forward as possible against the lug?
Reticle properly leveled?
Muzzle break locked down and properly timed?
Barrel nut torqued? not likely an issue unless it's actually loose.

Combine all of the with relatively cheap/crap 147gr ammo and a bad trigger.... Get some 165+ match ammo to see for sure what it'll do.

First thing I'd do would be remove the muzzle brake. Take that big heavy thing off is an easy variable to control. Why knows what it's doing to your harmonics, eh? Actually first thing I'd do would be torque specs on all hardware.
Click to expand...

Nope
Nope
Nope
And
Nope
The barrel was torqued on by a real gunsmith. I watched him do it.

I agree that it needs a better trigger and better ammo. I can make those upgrades for sure.

But, I will never take off that beautiful muzzle brake. I love it too much. It's my favorite thing about this whole rifle.

Taking off the muzzle brake would be like taking the stars off an American Flag. Haha.

If I knew 100% that the muzzle brake was the problem, I still wouldn't take it off. I'd just adjust my scope two inches to the left. That's how much I love this muzzle brake.
 
YeeHaa said:
I have had the same group results before with one rifle.
The rifle in question grouped very similar to what you're experiencing and my rifle was Very Consistent as well.
If I put enough lead down range it looked like I was running TWO rifles on one target.

After going back through anything that could cause this , dilemma, I discovered the the way the rounds chambered from the magazine up the feed ramp was damaging the projectile.
What I mean by a damaged projectile is it was getting slightly scored, point was slightly deformed as well. I am talking about slight damage, nothing severe enough to make the round not shootable at all.

I removed the firing pin and at various speeds cycled rounds through the rig. At Creep Speed I could see the ( my case the right round - mag fed) round hang ever so slightly and the bullet deformed ~ scored.
The left side feed ramp was fine and the bullet had no where near the damage the right side did.

Why? I attribute the two groups to different aerodynamics between the left & right mag feeds.

Concerning the Sightmark, while they are medium budget optics I believe the Triple-Duty line is stout enough to run on a Semi 308 rig.
I own one or two Triple Duty Sightmarks as well.

Safe Shooting
Click to expand...
This is probably it. Out of ~30 rds yesterday, I had several that did not chamber properly. When I tried to eject the live round, it was hard to pull out and the cartridge came out with a scratch down the projectile and a few tiny indentations on the cartridge. This happened 5 or 6 times. Each time, I re-chambered and successfully fired the round.

Today, I will feed and eject some rounds and see if I get any scratches or dents in the cartridges. If so, I'll take some pics and post them up.

I bet one of the feed ramps is sharp and biting every other cartridge. If so, I can polish the ramps and take it back to the range to test the results.

I knew this was happening yesterday, but it never occurred to me that a slightly mangled projectile would get thrown off course that much. I think this is probably the root cause.
 
Alabamacoastie said:
This is probably it. Out of ~30 rds yesterday, I had several that did not chamber properly. When I tried to eject the live round, it was hard to pull out and the cartridge came out with a scratch down the projectile and a few tiny indentations on the cartridge. This happened 5 or 6 times. Each time, I re-chambered and successfully fired the round.

Today, I will feed and eject some rounds and see if I get any scratches or dents in the cartridges. If so, I'll take some pics and post them up.

I bet one of the feed ramps is sharp and biting every other cartridge. If so, I can polish the ramps and take it back to the range to test the results.

I knew this was happening yesterday, but it never occurred to me that a slightly mangled projectile would get thrown off course that much. I think this is probably the root cause.
Click to expand...

Shoot a box just single feeding with no mag, that should tell the tale.
 
Alabamacoastie said:
But, I will never take off that beautiful muzzle brake. I love it too much. It's my favorite thing about this whole rifle.
Click to expand...

The idea behind taking it off would be only to rule it out as causing the problem. Not suggesting a permanent removal.
 
Tim said:
The idea behind taking it off would be only to rule it out as causing the problem. Not suggesting a permanent removal.
Click to expand...
Haha. I'm so glad you said this. I thought you meant take it off forever.
 
Alabamacoastie said:
Haha. I'm so glad you said this. I thought you meant take it off forever.
Click to expand...


I choose not to comment on my wife's clothes, my mother's cooking or another man's firearm accessories. No matter what my personal opinion is in regard to their poor taste.
 
Alright guys and Millie...

I just got back from the range and it's definitely the feed ramps scratching up the rounds as they slide into the chamber.

I started off shooting groups that I hand fed into the chamber. No magazine inserted... Here's my individual groups in order. As the gun and I got warmed up, the groups got tighter.

20190201_141156.jpg 20190201_142016.jpg 20190201_142657.jpg
 
Next, I loaded 10 shiny new rounds into the magazine. I then manually cycled each round into the chamber and out onto the ground, unfired. Every round came out scratched up... Long scratches descended from the tip of the projectile all the way down to the rim of the case.
20190201_143415.jpg 20190201_143431.jpg 20190201_143524.jpg
Next, I loaded these scratched rounds back up and successfully recreated the same left/ right groups that were happening yesterday.

20190201_144816.jpg
 
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Last, I went back to hand loading one round at a time, just to verify the scratched rounds theory... And with these last three rounds I shot the best group of the day and decided to quit on a high note.

I think, and correct me if I'm wrong, that I need to polish the feed ramps and any sharp edges leading up to the chamber and then take it back to the range for another battery of testing. I'll also check the lips of the metal magazine. I wonder if those steel feed lips are scratching my bullets...

Here's my last 3 round group of the day. I put that orange dot there to act as a new bullseye:

20190201_150139.jpg 20190201_150440.jpg 20190201_150455.jpg
 
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Alabamacoastie said:
I think @eddie0225 figured it out. We were just talking in chatbox and he mentioned that i need to make sure all of the oil is cleaned out of the barrel before shooting...

After sighting in, I sprayed a bunch of CLP oil directly into the chamber and barrel. That's when my shots started walking back and forth... it had to be all that oil.

What do you guys think about that? Sound feasible?
Click to expand...
dont clean that rifle everytime you shoot it. That's old tale crap. You can shoot 500+ out of that ar without cleaning and be fine.

I go a few hundred on my precision bolt guns. Now, when I do clean, and go shoot, the first round will always have a different POI, but it'll either be faster, or slower than the rest of my rounds I shoot. Your rifle will shoot better with a fouled better. Shoot it, let it cool, then shoot another group and see if it tightens up
 
Thanks for the pics. That's good info.
And personally, I've always had pretty good results with PMC ammo regardless of caliber. I consider it one of the better plinking rounds.
 
If you do the feed ramps yourself, take your time and do not remove a whole lot of metal at one time.
 
Tailhunter said:
Parallax on a scope can cause this problem.
Are you able to adjust it with the scope your using?
Click to expand...
I'm NOT speaking for Alabamacoastie , but for myself as I own Sightmark glass in the Triple-Duty Series.

While I do NOT care for an extra knob to turn ( Parallax ) , the Parallax on my Sightmarks are > S P O T O N<.
Spot On with the turret markings and the glass is fine.
No, I do not work for Sightmark.
 
I'm certain that the culprit has been found and it's the sharp edges of the feed ramp and chamber biting into the projectiles and therefore changing their in-flight trajectory.

I run science experiments for a living, and I think this is an open and shut case based on the fact that I was able to: 1. Prove that cycling the bolt scratches the projectiles. 2. Reproduce the exact phenomena from yesterday with the scratched bullets. 3. Make several fine groups and one fantastic group simply by hand feeding the rifle a single round at a time.

Myth Busters could not have done a better job on this case...

Thank you all very much for the great suggestions! I would not have known how to troubleshoot the issue without a few of you guys adding great insight and ideas.
 
Alabamacoastie said:
Alright guys and Millie...

I just got back from the range and it's definitely the feed ramps scratching up the rounds as they slide into the chamber.

I started off shooting groups that I hand fed into the chamber. No magazine inserted... Here's my individual groups in order. As the gun and I got warmed up, the groups got tighter.

View attachment 102950 View attachment 102951 View attachment 102952
Click to expand...
Love the "guys and Millie".....as if I had any single solitary idea what you guys are on about! I've never shot a rifle, though I've held some nice ones at my local gun store! I'm getting ready to google muzzle brake.....
 
jmccracken1214 said:
dont clean that rifle everytime you shoot it. That's old tale crap. You can shoot 500+ out of that ar without cleaning and be fine.

I go a few hundred on my precision bolt guns. Now, when I do clean and go shoot, the first round will always have a different POI, but it'll either be faster, or slower than the rest of my rounds I shoot. Your rifle will shoot better with a fouled better. Shoot it, let it cool, then shoot another group and see if it tightens up
Click to expand...
so you don't clean your gun and say you go a few hundred rounds on your bolt gun?? Question what did you clean your gun every time before you came here as you would always shoot at least 3 rounds to foul your barrel (what you said) or was it to just heat up your barrel to make it consistent? The only reason a person wouldn't clean their guns after every session is nothing but laziness in my book. Guess I'm old school you know a clean weapon is a good weapon. I learned this long before some idiot in the service tried to show me how to shoot. With today's cleaner-burning powders and all to actually foul your barrel, you'd need to shoot at least 10 rounds to even start to foul it. In actuality, all your doing is heating your barrel. It doesn't take a brain surgeon to figure that one out but call it what you want. Seems young people nowadays think they know everything and anyone older doesn't know their ass from a hole in the ground but eventually they learn just like we did. Glad you feel like you know what the actual problem is and have remedied it.
 
^^Jesus Grandpa..aren't you supposed to be outside shooting the neighbors cat again?
1) Torches a post for what he reads as a know-it-all opinion.
2) Proceeds to post a know-it-all opinion.
Lighten up Francis.
 
Alabamacoastie said:
I'm certain that the culprit has been found and it's the sharp edges of the feed ramp and chamber biting into the projectiles and therefore changing their in-flight trajectory.

I run science experiments for a living, and I think this is an open and shut case based on the fact that I was able to: 1. Prove that cycling the bolt scratches the projectiles. 2. Reproduce the exact phenomena from yesterday with the scratched bullets. 3. Make several fine groups and one fantastic group simply by hand feeding the rifle a single round at a time.

Myth Busters could not have done a better job on this case...

Thank you all very much for the great suggestions! I would not have known how to troubleshoot the issue without a few of you guys adding great insight and ideas.
Click to expand...


Yeah but Myth busters had prettier help.LOL
 
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