Pressure Signs?

[steve4102]

Sorry, I know this is Factory ammo, but I didn't know where else to ask this.

This is a photo of some factory case heads fired out of a New Alexander Arms 6.5 Grendel AR-15. Looks like high pressure to me, what do you think? The owner of this rifle is being told to "shoot away" or seat the bullets deeper on his factory ammo. The bullets are getting stuck in the rifling and an unfired factory round is very difficult to eject. What do you think, "shoot away"??



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[WESHOOT2]

No.
I think when bullets get forced into the rifling the gun needs more freebore......

[mrawesome22]

The bullets are getting stuck in the rifling

Are you absolutely sure about that? Can you see rifling marks on the unfired, ejected shells?

They look fine to me by the way. Primers look great.

[kiwi56]

Another method for checking for high pressure is measuring case head expansion with various loads.

[Slamfire]

This is 600 yard ammo I picked up from the AMU and USMC shooters beside me on Viale Range at Camp Perry 2007. I wanted ammo that really showed high pressure signs. Incidentally, it rained so hard I was blowing water out of my rear aperture, and the ammo was still wet in the picture.

As you can see, primers are leaking in the USMC and AMU cases, primers in the AMU stuff is blown, and the case heads are flowing into the ejector hole.

These are absolute positive indications of high pressure.
AMU Long Range Ammo

USMC Long Range Ammo


However, flat primers don’t necessarily mean squat.

Understand that I am a heretic. A total apostate, condemned to an eternity in hell for violating conventional wisdom. I lubricate the cases used in my Garands and M1a’s. I do this for increased case life, which is why I was able to take 100 cases, minus the amount the range gods hid in the weeds, for over 20 reloads in a M1a. No one ever takes brass that far without case head separations, I had exactly zero.

I found, using lubricated cases during load development I got nice rounded primers. As the charge increased, at some point the primer did flattenedout. However, if I started out load development with dry cases, I almost always got flattened primers. I did get rounded primers on extremely light loads, but starting in the medium light loads, I got flattened primers with dry cases and rounded primers with the same ammo with lubricated cases. After puzzling on this, I figured out that with dry cases, the primer backed out to the bolt face and then the case finally stretched back to the bolt face and stuffed the primer back in. So the primer was going to be rather flattened. The reason primers were not flattened with the lubricated cases was that the case was unable to grip the chamber walls and slide back to the bolt face before the primer was able to back out. As I reached my “maximum” loads, the internal pressures of higher loads flattened out the primers in the lubricated cases.

So what I learned about this was you will get flattened primers with loads that are not maximum with dry cases. I concluded that this was a good reason not to worry much about primer indications till they pierce or leak

Because primers lie.

[Lavid2002]

+1 Primer cup thickness can vary...

[Brian Pfleuger]

To add to the flat primers being meaningless...


In my 357sig using Federal "Match" primers and Power Pistol under 124gr Hornady XTPs the primers are flattened and slightly mushroomed at charges that are BELOW book starting loads, and continue to be flattened and mushroomed with no discernible change in severity up to book maximums.

[mrawesome22]

Correct. Flat primers usually have more to do with headspace. If you look at those photos, the primers are leaking. Definitely way over pressure, yet the primers aren't filling the pocket. Must have had correct headspace.

[SL1]

I don't think the primers are the issue in the OP's pictures.

What I see is impressions in the brass case head from features on the bolt face. To me, THAT is a pretty clear sign of high pressure. If he had taken case head diameter measurements before and after firing those cases, I suspect he would have found significant expansion, too.

SL1

[mrawesome22]

I thought all semi-auto's did that kind of stuff to the brass? Just looks like it's getting beat up to me?

[SL1]

Mrawesome22,

Maybe you are right about autoloaders. I only shoot bolt actions in rifle cartridges, and those would be clear signs of high pressure in a bolt gun. Anybody else have experience with autoloaders marking case heads like that?

As for primers, those don't look that flat to me. But, the Gendel is something like a 55,000 psi cartridge for an autoloader, right? So, I guess my expectations are from bolt gun cartridges with 65,000 psi SAAMI ratings.

SL1

[P-990]

With the Grendel, I would say those are overpressure, if only marginally, as the primers are still holding and not leaking. Probably originating from the bullets being stuck into the rifling (just going by the description). Does sound like the chamber leade is a bit short on that rifle.

Now, I am NOT surprised by the AMU and USMC 600-yard brass. Somebody dumped a dozen R-P brass on me at 600 at Perry in '05, thinking it was mine. The RIMS were being ripped along with the ejector marks. No shortage of nuclear loads on the 600-yard line with the .223 shooters. I try to not load mine quite that hot as a matter of course.