Need HELP on AR 308 Blown Primers

[smschulz]

Having a problem with blown/dropped primers on my MA TEN Build.
Issue with:
* Black Hills Red Box Match 168gn * Nosler Match 168gn

Tested with NO problems:
* HSM 168 HPBT Match * HSM 175gn HPBT Match * Privi Partisan 168gn Match
* Fed Gold Medal Match 168gn * Nosler Trophy Grade 165gn Accubond
* Winchester White Box 7.62 Nato 147gn (not accurate but no failures)

Rifle Specs:
* MA TEN Mono Upper
* Rainier Ultra Match 18" mid length 1/10 DPMS
* JP Rifles Enhanced Bolt
* DPMS Bolt Carrier
* Slash's Rifle Buffer/Spring AR10R-H (PRS stock)
* PRI Adjustable Gas Block

I am concerned ~ I have heard reports this is somewhat not uncommon on Gas Guns. I do not have this issue in my Rem 5R bolt gun.

I originally had a std gas block then tried a PRI adjustable and turned down the gas so the screw was a little more than half way covering the gas hole (maybe not enough?).

I lightly honed the chamber with 600 grit on a slow drill.

I checked the head space with GO, NO GO, FIELD Gauges and tested failed on FIELD, NO GO and Passed on Go.

Is this just normal on some ammo?
Should I send back to Rainier?
Do I just need to avoid certain amo?
Will going to a rifle gas port barrel be better?

Serverly Confused at this point?

This is wicked accurate but need to know what to do about the primer issue.

 

[tmpohuski7]

Re: Need HELP on AR 308 Blown Primers

over gassed.

 

[BCP]

Re: Need HELP on AR 308 Blown Primers

Super tight chamber, oil on bolt face/chamber?

What does fired brass measure at the base, shoulder and overall?

 

[MaximumVelocity]

Re: Need HELP on AR 308 Blown Primers

There are several factors that can play a role in gas guns for showing a hot load. Do you know what chamber was cut into the barrel? .308 chambers come in different sizes. Combine that with the gas system and your pressure signs can vary depending on the ammo. Gas gun ammo typically needs to be charged on the light/er side. Ammo that works in one may not work in another.

I have a gun that just doesn't like off the shelf ammo very much at all. It has a tighter chamber and this was expected. I can shoot FGMM 168 just fine. In fact, I still have yet to find a load that shoots better. It's a bit on the warm side but it's not blowing primers. FGMM 175 is way too hot and blows them every strike. I load my own ammo so I don't play with much shelf ammo but I do have 1 or 2 that shoot fine with okay accuracy.

Yes...this can happen and CAN be common depending on how your chamber/gas system was designed. Your best bet is to find a box ammo that your particular gun likes and maybe think about designing your own load and doing some development. Just stick with what works.

 

[trisurvivor]

Re: Need HELP on AR 308 Blown Primers

Having issues with my pof. It seems that it could be loose primer pockets. The inertia from cycling acts like a kinetic bullet puller on the primer. Are these reloads?

 

[P-Squared]

Re: Need HELP on AR 308 Blown Primers

It's hard to really say except the load is too hot based on what looks like the head going plastic and molding down into the ejector. Have you ever measured the chamber to figure out how far the land are compared to where the ogive in on those rounds? Maybe, just maybe, they're jammed into the lands on that barrel which is causing the over pressure. Just an idea.

 

[judgedelta]

Re: Need HELP on AR 308 Blown Primers

From looking at the pictures, the Black Hills rounds seem to have far flatter primers than the Nosler, but all seem to have cratered the firing pin indentation (except the ones that have blown out). Head spacing issue?

 

[dieselten]

Re: Need HELP on AR 308 Blown Primers

Turn your gas block in until the gun fails to cycle, then open it just a little

 

[amk]

Re: Need HELP on AR 308 Blown Primers

I have read before about Black Hills ammo has blown out primers.

 

[smschulz]

Re: Need HELP on AR 308 Blown Primers

A lot of comments all over the map.
Just goes to show you how perplexing the problem is.
I will try cranking down the gas a bit more and give it another shot.
Then maybe get another 20" rifle length gas barrel and hope for the best.
If still an issue ~ just will have to discriminate on ammo choices or maybe I will be reloading by then (the goal anyway).

 

[shootist2004]

Re: Need HELP on AR 308 Blown Primers

throw a suppressor into the mix and the variables multiply....

 

[pagana]

Re: Need HELP on AR 308 Blown Primers

Measure the diameter of your firing pin. It will likely be .078" or so with a hole in the bolt of about .080". They are simply too big. I had this problem with my .260 and simply bushed the bolt to a hole diameter of .060" and turned the firing pin down to .058". Problem solved, it would be hard to believe that Black Hills would distribute ammunition in quantity that exceeded SAAMI specs. In fact, when firing my handload in an out of the box rifle, it too blows primers that are fine in the bushed custom rifle.

 

[sapper12b]

Re: Need HELP on AR 308 Blown Primers

I have had the same issue with Hornady Super performance. Get a adjustable gas block. You have too much pressure coming back to the bolt.

 

[Petey]

Re: Need HELP on AR 308 Blown Primers

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dieselten</div><div class="ubbcode-body">Turn your gas block in until the gun fails to cycle, then open it just a little </div></div>

Yup, try this. A heavier buffer was also needed in my 308 carbine to keep primers in, but I'm not sure what's available in the way of heavy 308 rifle-length buffers.

 

[SSG3K]

Re: Need HELP on AR 308 Blown Primers

you have something that says dpms in your parts sheet remove and replace with a diffrent brand.

measure oal on 175 bullet
chamber the round using the rifle from the mag
remove and remeasure

i almost suspect very tight chamber (DPMS) or the ammo is non crimp and is seating deeper than spec (causes high pressure)


have expierienced this many times

 

[Jinete_Palido]

Re: Need HELP on AR 308 Blown Primers

Probably not what you want to hear, but I have a 20" Rainier Ultra Match with rifle length gas and I have the same problem, so going to that barrel/gas length may not solve your problem. I am still fiddling with it. I added an adjustable gas block, and still have issues. I get blown primers on Black Hills 168gr., and deep ejector swipes on most any other factory round or rounds loaded to factory specs. I am trying some downloaded rounds next to see if that helps. Sorry I don't have an answer to the problem.

 

[smschulz]

Re: Need HELP on AR 308 Blown Primers

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jinete_Palido</div><div class="ubbcode-body">Probably not what you want to hear, but I have a 20" Rainier Ultra Match with rifle length gas and I have the same problem, so going to that barrel/gas length may not solve your problem. I am still fiddling with it. I added an adjustable gas block, and still have issues. I get blown primers on Black Hills 168gr., and deep ejector swipes on most any other factory round or rounds loaded to factory specs. I am trying some downloaded rounds next to see if that helps. Sorry I don't have an answer to the problem.</div></div>
Yeah, that is not so good news.
Pretty much what is happening except that it also includes Nosler Match 168gn but other ammo shoots fine ~ looks like I need to consider another barrel mfg and forget Black Hills and Nosler. Fed Gold Medal Match shoots well for now until I get to reloading.

 

[M14]

Re: Need HELP on AR 308 Blown Primers

<span style="color: #FF0000">"checked the head space with GO, NO GO, FIELD Gauges and tested failed on FIELD, NO GO and Passed on Go."</span>

When you say failed on field and no go, that means that the headspace was too long or generous, therefore, it cannot pass go gauge if that is correct ? Or did you mean it would not close on no go and field ?

The firing pin suggestion is what you should follow, along with this: The gas operated system requires the headspace to be set such, that it allows 3-5 thousands of an inch, over case headspace length, for case expansion to extract and eject reliably. If your go gauge headspace check had "any" interference fit, or friction fit, it could be too tight and causing pressure to spike. Firing pin protrusion coupled with the tight headspace will most definately cause problems like you posted. Good luck and let us know what you find out.