AR 10 POPPING FACTORY AMMO PRIMERS

[del2les]

I had a "match" 223 chambered barrel for an AR do exactly this very thing using factory 69gr match ammo, and it was due to a short leade and tight throat. Since the barrel was not lapped from the manufacturer, I fire-lapped it with a Tubbs kit, and after that, no more issues.

 

[misterc01]

remember you need to watch for load compression. Also there are primer pocket gauges available for you to use to verify the pockets.

 

[Longshot284]

It's possible it's not "over" pressure. Depending on your gas system and the propellant Hornady uses in the Black ammo - if there's enough gas to start unlocking the bolt, the actual max pressure may be well within SAAMI, just a timing issue. Exacerbated by a suppressor I'm sure. If your gas block is adjustable you could back it down a notch. Or possibly something with buffer configuration would slow things down.

I would call Hornady Monday and explain the situation. They have been great to work with in my experience and should start a return for you to get the ammo back and pressure test it. That way, even if it tested fine, you'd know for sure what the pressure was.

Just throwing in another 2 cents - I know gas guns can be tricky sometimes!

 

[woodnut]

Well, I'm still in a quandary. I seated both factory and reloads til they didn't show any marks. still had pressure problems with the factory, but not as much. Did not shoot much, and only one round had lost the primer. Got heavy ejector marks on all factorys. Will go see my builder and let him have a crack at solving it. I am confident he will.
I think I could re-seat my reloads, but I hate to as they were shooting lights out in my bolt guns! I had hoped this build would shoot factory and I could shoot my reloads in the bolt guns. Now,my hope is he will solve it and I can shoot either in the gas gun.
Wish him luck!

 

[mudygmc]

Have your builder look for a reamer with longer freebore. Bring him some factory ammo with the gun. He coyld get exact specs needed by measuring them. When i ordered my Criterion 6mm creed. There was 2 different freebore specs. Builders are aware of the long hornady ammo. Should be an easy fix.

Adam

 

[KyCarl]

Isn't the Black line their economy line? That might explain it.
try some other brand.

 

[woodnut]

Thanks Adam, I do plan on taking him both factory and reloads to test. I do know he used the same reamer for both my bolt rifles and the AR, so there could be a need for a longer throat in the ARs chamber. He's very thorough and suspect he will find the solution.

 

[woodnut]

Yes, it is the cheap line. However, it shoots incredibly accurate in my bolt rifles. Chrono tests show it to be very consistent too.

 

[knighthook]

My brother has a Dpms light weight hunter in 260 rem. Factory ammo I believe it was 120gr federal were fine. He loaded some berger 130s to mag length and was blowing primers at 42gr of h4350. Closer inspection showed that the bergers were jamming the rifling. Setting them back made all the difference. No more blown primers at 45gr even. I recently had a 6creed barrel built for a savage. When ordering the barrel there were two options for freebore. I don't remember the specs offhand. But say one was like .087 for most all ammo. The other was .1xx for hornady ammo. I bet you any money your jamming the bullet and switching ammo or handloading will cure the problem. To try take a Sharpe and color the bullet. Then chamber the round and remove. Odds are with hornady ammo you will have rifiling marks on the bullet. Good luck figuring it out. Hope this helps some.

Adam

Adam, Great idea! I change to a different bullet an I started poping primer during load development. This was what was going on with mine!! Tks Frank

 

[Darryle]

Just for giggles, is the bolt/BCG a standard 308 or the HP version? I only ask because Toolcraft offers a Creedmoor HP BCG in Nitrided, DLC coating and Nickel Boron.

When shooting the 6.5 Creedmoor reloads with the original 308 BCG I had hard extraction issues and primer cratering, swapped to the HP bolt on the recommendation of a local gunsmith, no more issues. Both bolts were the Toolcraft DLC versions.

 

[dfanonymous]

Recently, I had an AR10 rechambered by a fine smith from 6x47Lapua to 6 Creedmoor. Went to test and zero it and two factory rounds had their primers blown out. Inspecting the primers showed no other pressure sign, but was black round it and the pocket was all black. Only two out of maybe 6 rounds. Other fired cases showed no pressure signs. Rifle operated normally.
I'm hoping ammo was at fault. It was Hornady Black, and I've never had anything like this to happen b4. But what do you think could have caused it?

You need a HP bolt. It's more common the you realize with 6.5 and 6mms.

I only know of two, JP and aero. I have an aero, and it works fine. Never had a primer issue.

 

[sea2summit]

Just PSA Federal says none of their .260 ammo is suitable for semi autos...found out after I tried three types in my AR 10 $80 later....

 

[Frog4aday]

Seems like I was hearing about pierced primers in AR-10 (SR-25s) when I was building my .338 Federal (AeroPrecision), mostly in the .260 Rem/6.5 Creed guns. The consensus was the firing pin hole in the bolt was a 'tad' too big, so you need a smaller hole in the bolt and a smaller firing pin to match.

This thread got me thinking about that so I did a Google search and came across this from the Western Powder page. You really need to click the link and read the whole thing, but this excerpt below gets to the heart of the matter.
http://blog.westernpowders.com/2019/02/cratered-and-pierced-primers-in-the-308-ar-family/
"Cratered and pierced primers" is not uncommon even in bolts guns. The most common solution is to reduce the firing pin aperture and firing pin diameters. There are vendors that provide the service of reducing the firing pin and aperture diameters ("bushing down the diameters") in bolt guns such as Gre-Tan Rifles. A simple analysis shows that a .0625" diameter firing pin aperture is 42% smaller in cross sectional area than the standard AR10 .082" aperture and will reduce the linear force the same 42% on a primer cup over this aperture from 317 pounds to 184 pounds assuming a 60,000 psi chamber pressure.


JP Enterprises is one among others that provide a solution for this issue. JP describes their solution as a "high pressure" Enhanced Bolt™ for the .308 AR. It has a .060"-062" diameter firing pin and firing pin aperture (see Figure 5 and 6).

 

[OhYtD]

Had the issue with 300 BLK. Had the time to compare sub to supersonic only using different brands. Not an apples to apples comparison by any means but in sub there were zero issues. Need to get another brand of super to confirm my gut feeling of bad primer size or pockets.

Factory assembled WW upper.