Why You Need To Keep Your M4's Castle Nut Tight

by Sarge, Tuesday, May 01, 2012, 23:05 (4386 days ago)

So I get a call from this guy I know, generally a real calm sort, and real safety-minded when it comes to guns or anything else. He's a little worked up. Says he just put a round in the dirt about 4" in front of his big toe. I say "Well heck, at least your muzzle was off your personal assets. Finger off bang switch Amigo..." He says "NO, I didn't have my finger in the trigger guard. You need to look at this thing! All I did was rack a round up and BOOM."

Well yes, by golly I DO need to see that. The halves get separated and here's what we find-

Closer...

and finally...

The castle nut could be turned easily with your fingers and the buffer tube was backed out clear of the detent port. When he racked the round up, the detent finally popped out and the buffer over-rode the hammer & knocked it out of engagement with the sear. If you look closely at the middle pic you can see where the hammer scored the face of the buffer when the rifle fired. The detent ended up in front of the hammer, captured when it returned forward again.

This is reportedly a relatively new DPMS A-15 with less than 100 rounds through it, used by two brothers at different times. I don't know whether the castle nut just wasn't tightened properly at the factory or if somebody had their fingers in it. I won't speculate. I do believe this is an unusual, mechanically caused accidental discharge. Thought I'd share it for the informational value.

Oh, and the lower wasn't damaged at all. The rifle was reassembled properly and passed all function and safety checks. Test fire this weekend.

Right now, I've got a double-back to day shift. Check in over the next couple of days.