Wierd Malfunction with Colt CM762-16S 308 Rifle

[Leadslinger585]

Took my AR10 out to a carbine course (read about it here: link) Approx 400 flawless rounds fired in the class. Haven't cleaned it since the course, but I took it out to the range today anyway. Before I started shooting, I put a couple of drops of oil (about 6 drops) in the bolt carrier holes as Kyle Defoor demos in one of his YouTube videos.

Other than a different stock and pistol grip, everything is OEM. Running 20 round PMAGs and Hintenberger surplus ammo.

Started practicing some drills and about 60 rounds in had a failure:

Fired a round, felt some peppering on my support arm and the bolt locked back. Went to do a reload and hit the bolt release, but the bolt wouldn't run forward. The release button was "dead". Removed the mag and saw that the bolt carrier had somehow bound up in the rearmost position (about 1/8" behind the bolt catch).

Tried to wiggle it loose with my finger and a bic pen, but wouldn't go. Took removing the front take down pin and wiggling the two receiver halves to get it to release and run home. Fired a few more rounds (about 40) with no more issues.

Anyone know what happened, and what the fix would be to prevent this in the future?

[Pappabear]

Look for a primer is the action. Good possibility. When you blow a primer shit happens.

Hintenberger, nope !

PB

[RHINOWSO]

Definitely look for debris in the weapon. I had some intermittent failure to fires in my SCAR 17 once and it turned out to be part of a broken feed lip floating around the action (batch of poorly heat treated FN mags, they replaced them no issues).

I've seen primers do that as well in a buddies 308 semi (make I don't recall). 2 primers floating around the action and the BCG gave him a hell of a time.

[Leadslinger585]

Took the rifle apart to look for the blown primer and found the issue (I think)

The cotter pin somehow worked loose and sheared off!

[Tx_Aggie]

I doubt this fits what most people would consider a "Catastrophic Failure."

Glad you're ok and that the rifle seemed to go back to functioning after you got the BCG free.

[opngrnd]

I'm glad you're ok. I'd be interested in how the FPRP(cotter pin) ended up that way.

[Leadslinger585]

I doubt this fits what most people would consider a "Catastrophic Failure."

Glad you're ok and that the rifle seemed to go back to functioning after you got the BCG free.

Maybe my definition of catastrophic failure is not the same as others. FOr me if a malfunction can't be fixed with the removal of a mag and few racks of the charging handle and requires messing with the take-down pins, that's catastrophic. For me anyway.

[AKDoug]

Catastrophic is shit blew up and is not repairable.

A stoppage is something that can be fixed with quick remedial action.

A malfunction is something that needs to be repaired, which is what you had.

Hard to see from that pic, was the pin installed in the correct direction? Did you remove it at one point?

[Leadslinger585]

Gotcha, thanks for clarifying that.

Pin was installed with the "head" of the pin on the left side of the bolt. And yes, I had removed it for cleaning.

[m4luvr]

I hope it wasn’t a cotter pin - they aren’t used in these rifles - only a proper firing pin retaining pin will do. BCM has them.