Former Grendel

[LR1955]

Definitely looks like out of battery based on the way the case split. I agree on the 120 AMAX, just problems with the Grendel exactly as you described.

One question: I have read that a firing pin strike out of battery is not technically possible with the AR design as the pin is not long enough unless fully in battery with the bolt fully back in the carrier. Which can't occur out of battery.

PG:

You are right. The inertial firing pin / bolt design themselves are intended to ensure such things do not happen and unless something is way out of spec with the firing pin or firing pin hole, they alone aren't the cause.

However, combine a functional firing pin / bolt assembly with a couple of more issues and the ingredients can combine to cause the out of battery firing. I am pretty convinced that the 120 AMAX bullets had to be seated in such a manner in order to feed and shoot that they were probably the baseline reason why it all happened. Most likely another ingredient was a primer not fully seated. However it could also be the one in 1M primer that was weak or sensitive for some reason and that, combined with it not being fully seated, combined with a firing pin on the edge of specs, ...... etc. You guys get the picture.

I would also view a high primer as far more possible if he used a progressive press or seated the primer on a regular press primer feed arm thing than if he seated the primer by hand.

I doubt it could be replicated with any predictability. The problem with out of battery firings is figuring out the cause.

LR1955