.308 case neck tension and crimping

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glennv

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I was testing some rounds in my M1A to see if the OAL was changing while in the magazine while being fire. Placed 10 rounds in the gun, fired 9 and checked the OAL of the 10th. Length changed between .005 and .008 each time. Did the same thing but this time checking the 10th round after the 8th was fire, therefore exposing the 10th round to the inertial forces while in the mag but never being chambered. There was no measurable change in the OAL.

So clearing the OAL is changing do to clambering. I had two batches of ammo that I loaded up, one no crimp and another with a light crimp. So is it safe to assume that I should keep crimping a dummy round until there is no OAL change?
 
I'm interested in what the experts might say as I'm also reloading for my M1A and recently stopped adding a crimp. How many reloads do you have on the brass you were testing?
 
I'm interested in what the experts might say as I'm also reloading for my M1A and recently stopped adding a crimp. How many reloads do you have on the brass you were testing?

I used once fired brass.
 
Hi. I loaded for a semi'd Winchester M-14 for eons(up until our rectal orifi government followed the ATF's idiotic idea of 'Once an MG, always an MG.') with no crimping. No fuss either.
Your 'once fired' all the same brand? Some brands are softer than others. Federal, for example, is known for being softer. That just means it doesn't last as long.
Your cases aren't getting sized quite right if the bullets move. Most likely the expander is opening 'em a tick too much. You could check its diameter.
Crimping tends to be detrimental for accuracy. Mind you, that really only matters if you're loading for match shooting.
 
Sierra Bullets proved back in the 1950's that crimping rifle bullets in case necks degrades accuracy. Their current 22 caliber match bullet that's cannelured because so many people wanted it, is not tested for accuracy specs in crimped cases; they shoot about 1/4 MOA less accurate because of that crimp.

US military arsenals used to crimp 30 caliber bullets in their match ammo until competitors finally convinced them to quit. So they stopped putting the cannelure groove in the 172-gr. bullet and crimping case mouths into it. Much better overall accuracy.
 
So would you say crimping has more of a detrimental affect on accuracy than variations in OAL caused by recoil and inertia of an autoloader's action ?
 
When I load 308 for my AR-10 or M1A I look at having good and consistent neck tension. That is all I want. I experimented with crimp during the early 90s going so far as using a Lee FCD (Factory Crimp Die) and while I didn't document everything it didn't take long to see my groups opening up when shooting the crimped with the same loads that always grouped good for me. Tried a crimp and as was expected got poor results, abandoned it and never bothered to crimp bottle neck rifle again. As mentioned, I rely on good and consistent neck tension.

Ron
 
Yes, I would say crimping has more of a detrimental affect on accuracy than variations in OAL caused by recoil and inertia of an autoloader's action. That was proved when people handloaded new cases used in both Garands and M14NM and M1A match rifles. Those rounds had less release force (neck grip on bullets) than crimped in match ammo case mouths as well as asphaltum sealant making bullet's "well glued" in case necks. None of the commercial match ammo used in those semiautos had crimped in bullets. Military team members often seated those glued in arsenal match bullets a couple thousandths deeper in the case necks so the neck grip was both less and more uniform. Accuracy was much better and no bullets shifted from recoil. Same thing with replacing the arsenal bullet with a commercial match bullet for better accuracy.

But there's folks that don't suscribe to such facts; they have their way of reasoning and nothing will budge them from it. In spite of millions of rounds fired in semiautos proving otherwise.
 
Well, it's the feedback here that resulted in my not crimping so I'll continue to not do it :)
 
Mr Bart is correct about crimping causes accuracy problems, both to the bullet itself as well as the crimping process. Attached is a photo of vintage military match ammo loaded for the Garand, note that it is not crimped, as arsenals were well aware it was not good for accuracy (Neither were the primers.) Had to chuckle at Mr. Barts memory of "popping" the seal on ammo. I was with AMTU back then and we all carried a Lyman "nut cracker" tong tool in our shooting stools to pop the seal on ammo issued on the line at "leg" matches. Those were innocent times.
 

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I too used a Lyman 310 tool to crack M118 match ammo.

The DCM/CMP rules stated (until about 1990) that unaltered issued ammo be used. I've seen leg hunters in EIC matches have their scores disqualified because they "cracked" that issued ammo and therefore altered it. I only shot cracked stuff in NRA matches.

Some folks have earned the points and awarded Distinguished badges without firing a single shot in a leg match.

Regarding reloads per case limits for .308 M1 or M1A semi autos. 5's about the limit if fired case shoulders are set back .003" for good functioning. Less if fired cases are resized more so.

Nobody shooting best scores in matches with these rifles does so with reloaded cases from one unless their bolt face is squared up with the chamber axis. A new case has its head smashed out of square when first fired. Resizing one doesn't square it up. That causes worse problems if cambered again and indexing 180 degrees out from its first position. Shots from such cases tend to string from 7 to 1 o'clock on target. New case heads are pretty well squared up and don't have such problems.

I don't know of any such bolt facing on those rifles; military shops never did it as far as I know.
 
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