Does this look similar?
That is from Carbon Arms facebook page, October 29, 2013. Part of an article I wrote for RECOIL that will be in the SHOT show issue. Deep seated, 77 grainer in front of a compressed load of fast pistol powder. NEW upper, receiver, BCG that were all subjected to extensive NDT protocols and tests. I also put a slug in the bore of an M4 about halfway between the gas port and the chamber, then put a 77 grain 5.56 load in and fired, no failure, fired again, no failure, fired again, no failure. The 4th round cleared the bore and we put 4K rounds through the M4 on FA with nothing. The X-ray images of the barrel bulge will be with the article.
First, highly unlikely anything was wrong with the rifle. In order to blow the bottom of the carrier off, the bolt had to fracture as well. Adding up the bolt, carrier and receiver strength, the loads to cause that damage are over 200Kpsi, or about 4 time operating pressure, or 3 times proof pressure. BAD AMMO!
I've blown up 15 firearms, 8 cars and 7 houses...on purpose and not illegally with overlapping safety protocols, in the course of my professional work. Still never turn down the opportunity to make something go boom.
When I was testing propane tanks for a major national supplier due to a HMS inquiry, I had three firemen huddled and wide-eyed behind their pumper truck. It was kind of funny.