factory 220 grain .300 black out pierced primers

[DFBrews]

I was finally able to take out the .300 black pistol i built. everything worked fine when i was shooting the 115 grain rem factory ammo. But when i tried to run the 220grain sub sonics i of course had feed and extraction issues which i attribute to the h2 buffer i had in the gun. it is to heavy for the load i was sorting my range brass and found a pierced primer pocket on 3 of the sub sonic spent shells. i remember one of the shots I saw a flash out of the ejection port on the second to last shot of the mag.

I also noticed that on some cases the primers are flattening and slight swipe marks. but not all, do not know whether these are sub or super sonic.

upper is a 10" houston armory barrel dpms upper nibx carrier group.

what can cause pierced primers assuming the ammo is not the problem.

right three shells are pierced and the upper 3 are flattened.



IMAG0967 by post_james86, on Flickr

[Zombie Steve]

Is the tip of you firing pin jacked up? One pierced primer can do it and cause others....

If the firing pin looks ok, I'm guessing overpressure ammo.

[Danimal]

There are a couple things that I am running into with my 300 BLK. One of them is that the chamber is too tight. I get cases jammed in there so tight that have not even been fired because bolt failed to close fully. The other problem that I am finding out is common are the sub-sonic bullets are actually being jammed back further into the case when the round is chambered. This happened to two of mine, and because of the tight chamber my bolt failed to close and I was able to extract the rounds to look at them.

If they are being driven back into the case and resting on the rifling when you fire then you would definitely be getting close to piercing a primer. That is about the only thing that I could think of though, because the sub sonic rounds are only supposed to run less than 30,000 psi depending on the bullet if I remember right.