I’ve seen a few, but nothing quite as “exciting” as this one.

The worst two I ever saw were on raare and exotic rifles; a SiG AMT and a genuine ex-Portuguese AR-10, both in 7.62 NATO.

BOTH owners were using reloads.

Fortunately, the damage was not as catastrophic as the illustrated AR-15, but ugly, none the less.

When both were carefully dismantled and examined, the fired bras showed a wildly enlarged primer pocket and distorted head.The big clue was the neck. In both cases, the very end of the neck was “featheredwith a thin ring of an extended brass “flashing”.

It appears that both cases had “missed” case trimmong and were over-length, but not to te point the chambering force of the return spring would be insufficient.

So, the end of the neck was “crimped” deeply into the bullet, right at the beginning of the throat / leade.

In a basic bolt-action, a firer might just notice a round that was resisting being chambered and thus hopefully NOT try and hammer it in, but eject it for later examination.

One of the engineering bonuses of the AR platform is the Alloy receiver. This is more of a “shell” than something like the M-1A type. In the AR, if the bolt-head and barrel extension are to spec, they may “hold” and the the barrel will be blown out of the extension. Bear in mind that, if there is a wild over-pressure in the bore, the bolt WILL unlock at a bout the same time the case is startiing to “flow”; REALLY NASTY!!: A massive rush of gas from a ruptured case, surging back into the “works”.

The alloy upper and lower will be wildly bulged and maybe torn, but will not fragment like a grenade. This is not unlike the difference between steel and Aluminium SCUBA tanks. Neither type was known for regular, catastrophic failure. Poor maintenance and handling probably destroys more SCUBA tanks, guns, cars etc. than the mere passing of time.

Trim your brass and double-check how much of what powder you are shoveling into those cases!!

Brass cases, gauges or verniers, trimmers and powder scales are a LOT cheaper than eyes and fingers.

What is a duplex load and what and how much powder was used so we can all learn what NOT to do?