6.5 Creedmoor AR10 primer cratering

[Lion Armament LLC]

This one has me stumped...
SLR receivers and adjustable gas block. Elftmann trigger. I've tried combos of Proof (stainless) and Bartlein barrels with JP and Lantac BCG's, and a matched bolt with the Bartlein. Federal 120gr FMJ and 140g SP are showing cratering, flattened, and an occasional pierced primer. Barnes 120g TSX was fine.

Is Federal 6.5 loaded hot??

[QuietM4]

Suppressed or unsuppressed? Head space verified? Ejection is OK? Is the gas block properly adjusted? Do you have a chronograph to measure the FPS of the Federal vs the others?

[Lion Armament LLC]

Unsuppressed. Yes headspace verified. Haven't been watching ejection. Yes to GB. No chrono data.

[Jack Dupp]

A strong possibility is your firing pin isn't a good fit to your firing pin hole in the bolt. Think hotdog down a hallway.

[Lion Armament LLC]

A strong possibility is your firing pin isn't a good fit to your firing pin hole in the bolt. Think hotdog down a hallway.

I hear you, though it seems odd it'd be the case with two separate BCG's, and on the Shilen a third matched bolt/pin that came with it.

[QuietM4]

Don't shoot Federal ammo, simple solution.

[Lion Armament LLC]

Don't shoot Federal ammo, simple solution.

Thought of this

But honestly, is this a known thing with Federal ammo, or is it an underlying issue with the firearm?

[QuietM4]

Could just be the Federal ammo, but I’ve never heard of any issues. If it was a mechanical/parts issue, it would do it with all ammo, not just the Federal….that is the common denominator.

[Lion Armament LLC]

Could just be the Federal ammo, but I’ve never heard of any issues. If it was a mechanical/parts issue, it would do it with all ammo, not just the Federal….that is the common denominator.

I hear you. I'd rather it just work with everything that is within spec. I'd be fine with saying not to use X obscure brand if they were known to just make stuff that's too hot...but it's Federal. I'll explore it more though. Thanks for the input.

[BigNate]

Are there any other high pressure signs (extractor / ejector marks, signs of case stretching, etc.?)

No clue what the cause is... but I can tell you what I would do to try to find the issue...
1) Pick one configuration of the gun - and confirm that it is in spec (check headspace / chamber - confirm with go / no-go gauges).
2) If you have a cartridge that you know and trust because you've shot a ton of it - preferably something that is a middle of the road cartridge - I'd take a box of it and tune the gas system to it as a baseline. Get the gun ejecting in the 3:00 - 4:30 ark and confirm no pressure signs, etc. If you DO have pressure signs or trouble getting the gun to group brass - stop and look more closely at the gun.
3) Given that it's 6.5 CM - not something obscure or super expensive - I'd buy a box of a bunch of different grades of ammo ranging from white box to good hunting stuff and including the Federal stuff that you are having trouble with - then get a chronograph and maybe a big tarp or two and go shoot it all. Record:
a) Velocity / SD / ES for each load
b) Where the brass is being thrown for each brand/load - direction and distance - take notes.
c) Pressure signs on the brass. If it were me - and I saw anything else go out of norm (velocity, or brass placement) I'd stop - and start recording each round individually and checking each case for pressure signs.
4) Compare your velocity data to both the box for that load - and to other similar products. Look for patterns - and for things that obviously break the pattern.
If you find that everything except the federal shoots fairly close to the advertised / expected velocities, and ejects in a pattern that is either "good" or perhaps consistent with what you are seeing in the velocity data - then you have your answer - it's the federal ammo. If you find that the negative signs are occurring across a variety of rounds - then look for the next pattern...

At the end of the day - the whole exercise is about changing just one thing until the issue is isolated.

Just my 2 cents.

[QuangTri]

FWIW, my ancient DPMS bolt and firing pin exhibited "cratered primers with commercial (not with surplus M80) .308/7.62mm ammo.
Never saw a pierced primer, but the crater bothered me. Got a JP high pressure bolt and the cratering vanished.
I put it down to a sloppy firing pin hole in the DPMS bolt. I would call it more an extrusion of the primer.

[Lion Armament LLC]

Update, it was the ammo. I tried seven different loads. The three Federals crated, the other four (Hornady, Barnes, Sig, & S&B did not).

[QuietM4]

Update, it was the ammo. I tried seven different loads. The three Federals crated, the other four (Hornady, Barnes, Sig, & S&B did not).

Interesting. I wonder if the Federal primers are somehow thinner, compared to what the other ammo mfgs use. It's been a while since I used Federal primers, but I never had any issues like you experienced.

[blasternaz]

Used to be the only primers that reliably worked in light revo actions were Federals. Seems they still are the thinnest.

[Doc]

Update, it was the ammo. I tried seven different loads. The three Federals crated, the other four (Hornady, Barnes, Sig, & S&B did not).

I’ll swing over and collect the defective ammo for ya. I won’t even charge you for disposal