6.5cm blown primer factory ammo AR10 platform question

[rockwind1]

UPDATE: SOLVED PROBLEM i have tried a different factory ammo,, hornady with a lighter bullet and it works exceptionally well now. PRIMERS STILL A LITTLE FLAT, VERY FAINT EJECTOR MARKS, NO EXTRACTOR MARKS. doing happy dance.

THANKS FOR ALL THE INFO AND HELP
situation: hoping this isn't a stupid question. maybe just the gas block.
bought a very low round count ar10, decent components, Criterion 16 inch barrel. JP matched high pressure bolt. JP silent capture springs. Rise Armament Trigger, unknown adjustable gas block,

anyway,, when i got it, i put a 338ba suppressor on it that i wasn't using, and used fgmm 6.5 factory 130 berger hybrid OTM ammo. i put 10-15 thru it with a trij mk3 and then got squirreled. it shot great and no probs. 2 years later, circumstances made me want to revisit it, but i put on a ultra 7 .30 cal suppressor. I don't remember dicking around with the gas block last time. anyway,, it seemed like a lot more gas than usual went in my face but i didn't remember exactly from 2 years ago so, i shot again and it didn't cycle right. looking in the mag and found a blown primer. so i think it clogged up the mag. i picked up the 3 cases and sure enough a blown primer, also the primers look a little flat,, and decent marks on head.

i mean, i have seen flatter primers, it doesn't look too bad. but
i know ar's are pretty hard on cases but having a blown primer seems extreme. my thoughts are maybe the smaller suppressor caused more gas build up,, perhaps i should adjust gas block but it still seems a little weird, it's just factory federal ammo, how hot can it be?

appreciate any thoughts. merry christmas to all!

 

[RegionRat]

Flat primers + ejector imprints + soot + blown primer = Full Stop and investigate

These are all high pressure signs. Do Not Test Again till you determine the root cause. If you can't debug this, get help.

 

[jelenko]

Do I have it right that there is brass missing from the bottom of the primer pocket? In the pics, it looks like there are pieces missing! If so, unless the case was defective, that's a lot more pressure than just blowing a primer out.

ETA. Nevermind - I can see all of the bottom of the primer pocket in the first pic after it's enlarged.

 

[Kracken McGraw]

it's just factory federal ammo, how hot can it be?

Pretty darn hot evidently.

 

[jepp2]

it's just factory federal ammo, how hot can it be?

1. you blew a primer
2. you have significant brass flow into the ejector opening
3. you primers are extremely flat

Federal can load their cartridges to the SAAMI max of 65,000 psi. Your pressure indications show in your rifle you are well beyond the maximum pressure based on 1. 2. & 3. Clearly in your rifle configuration, those factory loads are unsafe to shoot.

 

[linedrive301ft]

Do you have a bore scope? Check for a carbon ring.

 

[rockwind1]

Do I have it right that there is brass missing from the bottom of the primer pocket? In the pics, it looks like there are pieces missing! If so, unless the case was defective, that's a lot more pressure than just blowing a primer out.

ETA. Nevermind - I can see all of the bottom of the primer pocket in the first pic after it's enlarged.

great, thanks. as far as i can tell, only primer itself blew out.

 

[rockwind1]

Do you have a bore scope? Check for a carbon ring.

I do and i will.

 

[rockwind1]

Pretty darn hot evidently.

hotter than i would have though, but is there any fairly common mechanical thing on AR10's that would cause this vs the factory ammo?

 

[rockwind1]

Flat primers + ejector imprints + soot + blown primer = Full Stop and investigate

These are all high pressure signs. Do Not Test Again till you determine the root cause. If you can't debug this, get help.

I agree, glad I posted. i thought they looked a little flat but wasn't sure how flat.

 

[rockwind1]

so, further research has me leaning towards increasing buffer weight and adjusting gas block, will also put my 338 supressor back on.

 

[markm87]

AR10s are nothing but ass ache in my experience. We get this same thing with an LMT 308.

I'd be adding some chronograph testing to your research. A heavier buffer will do nothing to reduce the pressure spike. That will only slow down the bolt speed.

If this were my gun, I'd work up a handload and stop shooting factory stuff.

 

[RegionRat]

but is there any fairly common mechanical thing on AR10's that would cause this vs the factory ammo?

AR10 (SR25) are not as standardized as an AR15 pattern, but the rifle pattern itself isn't usually to blame for overpressure.

We start by inspecting the bolt/chamber/barrel which is agnostic to all the mechanisms of the action in this context. And the buffer has little or nothing to do with this since the event is over before the bullet passes the port and before the bolt rotates.

Start with the advice above and scope that chamber and bore. Then inspect that chamber and bore.

You may have a mess in the bolt, so I would also take a long look at the firing pin channel and the ejectors and the extractor. Did we account for the blown primer, or is that lurking in the trigger group where it may cause grief later?

If there is no evidence of a cause in the barrel or chamber, check the assembly for headspace.

ETA: is the history of the suppressor known? Is there any evidence of an obstruction or blockage in the suppressor? Was it wet?

If all that checks out, then the ammo is the next order on your agenda.

Do not attempt to fire the weapon till you have thoroughly inspected it. If you don't have the resources to inspect it, get help. If the weapon checks out, then the ammo should be set aside for disposition that doesn't involve risking your eyes and fingers. Play it safe and good luck.

 

[Walt Krafft]

Completely clean and inspect the rifle. Then shoot it without a can. If it shoots well without the can, add the can and see what happens.

 

[nmkid]

Federal factory load. Called Federal, and they said it was fine after looking at the picture!

 

[Idaho-Lefty]

I SERIOUSLY Doubt that,.. it's an Ammo problem !
Usually, every Lot of Ammo IS, Tested at Factory, before, shipping.
Have a Friend, shoot a couple, in a Good, Bolt action First, before complaining to, Factory.
Probably have,.. a "Can" Pressure, Issue !

 

[rockwind1]

I SERIOUSLY Doubt that,.. it's an Ammo problem !
Usually, every Lot of Ammo IS, Tested at Factory, before, shipping.
Have a Friend, shoot a couple, in a Good, Bolt action First, before complaining to, Factory.
Probably have,.. a "Can" Pressure, Issue !

i am going to do that!!!

 

[dellet]

If everything is the exact same as two years ago, including the ammo, except the suppressor. I would suspect the ammo.

The suppressor would cause cycling problems, extractor marks, stretched case. the added back pressure will not pop a primer. Easy enough to prove by firing without.

Ammo sitting on the shelf, maybe questionable storage, can cause the dreaded “bullet weld” to the case neck and that certainly will raise pressure. Loving the bullet a couple thousandths to brake the Weld will likely solve that problem of it exists.

If it’s different ammo, you need to determine if the new is high pressure, or the old was low pressure.

Don’t rule out two issues.
High peak pressure causing brass flow into the bolt face.
Cycling issues and swipes do to added back pressure from the smaller diameter suppressor.

Two completely different causes.
High pressure at the chamber blowing the primer.
High pressure at the muzzle causing extraction problems.

Generally speaking high pressure at the chamber, lowers pressure at the muzzle. That’s why you likely have two issues.

 

[ToddKS]

The issue is likely the suppressor rapidly fouling the barrel. I experienced this getting ready for a suppressor match earlier this year.

Clean the barrel and shoot it without the can. I expect the ejector swipes may go away. Federal primers are on the softer side. The case on the left in your picture is about what I would expect from normal Federal factory ammo. If this resolves the problem, then that ammo is likely not going to be compatible with that can.

 

[Rocketvapor]

I don't see swipes caused by AR gas action.
Just pressure signs. Imprint into ejector and extractor.
Opening too soon will cause swipes.
Head space/case head slamming into bolt will cause imprints and blown primers


I shoot a NO-GAS 22N in AR-15. Move gas block,or turn off, shoot one without can.