Thought I screwed up

KnotRight

Well-Known Member
Charter Member
Benefactor
Life Member
Joined
Dec 20, 2016
Messages
5,468
Location
Savannah, GA
Rating - 100%
4   0   0
Back in 2017 when I started reloading 300 BO rounds I was using the Hornady 9th edition manual. Have not shot over 100 rounds of 300 BO since I got my rifle but loaded over 250 additional rounds.
I getting a piston length barrel for the new build and started reload some more with a bunch of different bullets. Now I am using the Hornady 10th edition manual.
Looked at my reloading data (Excel spreadsheet) and noticed that everything that I loaded a couple years ago was well over the OAL in the 10th edition (same bullets) so I resized all the old bullets. While sitting at my desk the 9th edition was behind me and looked at the OAL. They were 2.215" and .100" longer than the new one.
Interesting how that changed.
 
Last edited:
COAL with subsonic 300BO is normally set using the bump in the AR magazine or the magazine itself.

Supersonic, MAX coal can be set using your particular firearm. Keeping in mind that not all rifles are the same with regard to mag size and throat depth.

Not 100% sure, but I would look carefully at the bullet type used in the different load data. One might use a new style tipped bullet vs a BTHP.
 
OAL is a parameter that can be tricky. The OAL you end up using should really be determined by the specific bullet you are using, and your particular gun.

For handguns, I always do the "plunk test" to know just how far out I can seat the bullet and still chamber safely in my gun, and I like to have at least 0.020" jump to the lands. And, of course, it has to be short enough to fit in the mag. I may adjust even shorter if I have to, for reliability in feeding and chambering.

For rifle, it is a little different determining the OAL, but generally you start out seating the bullet long and then keep shortening it until it chambers. Again, most people like 0.020" jump, but the amount of jump can affect accuracy, some bullets like more jump than others. For 5.56 ARs, this is rarely needed as the 5.56 chamber has a very long leade and the max OAL of 2.260" (for mag fit) will typically leave a long jump to the lands for all bullets. I have no experience with 300 BLK, though, so I can't help you there.

Changing from one brand of bullet to another, even if they are the same type (FMJ, HP, RN, FN, etc) will require going through this process all over, as each may have a completely different profile.
 
Along the lines of what was said above, OAL usually isn't something you have to go by according to a reloading manual.. It's a general reference that means ammunition loaded to this length should work in most any firearm. Some important things I can think of at the moment while experimenting with overall length.....

1. - Make sure your round will allow your firearm to go into full battery.... IE, Your bolt will fully close, your slide will go all the way forward etc. Best to do this with a dummy round (no powder, no primer) before charging any ammo...
2. If you are working with maximum or near maximum charges and your length is shorter than spec..... reduce the charge a little bit. Keep in mind what was said above...….. 2 bullets may have the same weight but different length specs due to the bullet design. A hollow point will usually be shorter than a spitzer or round nose bullet. Try to get the length for the bullet you are using as a reference point. In 300BO, I would imagine the 225 grains subsonics are quite a bit longer than the 110 grain hunting rounds......
3. If using a firearm with a magazine, make sure it fits into the magazine.
 
I've not been able to rely on book OAL when loading for my 300BLK rifle. I'm using funky bullets so that might be the issue, but I had to measure max OAL for myself and load with a little clearance.
 
Last edited:
Thanks for the replies but I am not sure I got a point I was trying to make. Please see below:
9th.jpg 10th.jpg
 
@Toprudder is correct in my opinion. For consistency the length from cartridge base to bullet ogive is the important dimension.

I only consider OAL when working with loads that I know are "hot rods", where pressure can be an issue, and then only in determining a starting point for load development when working with a bullet for which I cannot find similar data. In selecting a starting point, you need some idea of case capacity and the amount of displacement the bullet has inside the case. After that, it is all about looking for pressure sign.
 
BowWow, I just called Hornady and they said that the 9th edition manual is wrong. They updated the information in the 10th edition but still made a mistake in the 30 cal 150 grn SST. The OAL is stated at 2.210" and should be 2.100"
The representative basically said that the cannelure should be at the top of the brass. This it true using the 150 gn bullet in the 300 BO or a 308. I asked about the Match bullets without a cannelure. His response was the Match bullets are so long it should not matter and will be around the other bullets in that caliber.
 
Back
Top Bottom