I had an interesting situation arise with my Bushmaster here a while back that I thought you folks might find interesting.  

I was shooting some practice ammo through my A2 Dissipator late last year (just before the last match of the NCPCPL season) and had a primer blow out on a round.  No damage to the gun, so I take it apart, clean it and put it back together.  I then fired a few rounds to make sure all was well.

Cut to the competition.  I’m on the firing line, get six rounds out and all of a sudden the Bushy starts short stroking and I’m manually cycling the bolt trying to get my last 4 rounds out before time ends… fat chance.  I drop out of the match and put the Bushy away, too disgusted to work on it then and there.

Cut to February this year.  The Bushy has been sitting, nonfunctional since the last match. I break it out to prepare for the 2006 season, and the problem persists.  I take it to a local black rifle mechanic who replaces a couple parts on my bolt along with a badly worn gas tube and away we go to the range.  It’s STILL short stroking.  We swap out parts and narrow the culprit to the bolt carrier.  My shooting buddy and I tear into the rifle and make lots of small parts out of a couple big ones, dump everything in the ultrasonic cleaner and let it cook for 20 minutes or so while we detail strip my P226.  The only part we didn’t take off was the carrier key from the carrier, since we didn’t have a torque wrench.  We take everything out, reassemble and voila!  Nothing.  Damn thing is still short stroking.  I cart it home, thoroughly disgusted and begin costing new bolt carriers, which, for match grade stuff, is painfully expensive.  I decide to poke around the carrier again and take the rifle apart.  I inspect everything and can’t see any problems.  I attempt to blow through the carrier key and… no air.  Nothing gets through.  I get a fine pick and a flashlight, and start poking around in what should be the back of the carrier key and find an obstruction.  Oddly enough, the obstruction had a firing pin dimple and the appearance of brass where I scratched it with the pick.

Carefully I drill out the obstruction to find that this is the primer from that blown out round the year before, and it had somehow or another found it’s way into the carrier key.  It must’ve been in sideways at first, allowing enough gas to get by to cycle the weapon for 10 rounds or so, but then rotated in the key during the competition and slammed that door shut.  The subsequent rounds I fired after that while manually cycling the weapon served to coat the primer with carbon, hiding its color and making it very hard to spot.  It had made a perfect seal and I’m here to tell you, the outside diameter of a primer out of a .223 round is almost exactly the same as the internal diameter of the carrier key.  I reassembled the rifle and shot my first match of the 2006 season with no issues whatsoever.

Problem solved and my Bushy runs like a top once again.

Wow! That has gotta be a new one. Glad you found it. That kinda stuff can make you crazy.

What are the chances of that happening???

You didn't take a pipe cleaner and stick it in the tube when cleaning or try to shoot some cleaner into it. You know your having a gas problem and don't check the whole system out. What is worse the so called Black Rifle Mechanic and he doesn't check it. I would go back to him and ask for my money back.

As luck would have it, we didn't have any pipe cleaners with us at the time and we blew through (or though we did) the carrier key with an air compressor.

Lesson learned, that's for sure.

That one goes down in the books thats for damn sure.

Why didn't you swap bolt/carrier with someone the first day, to localize the problem?  

No time to troubleshoot.  Other matches flights and matches were progressing.

Quit eating Bushmasters and they'll quit giving you gas problems.

Just kidding, what are the odds of that happening?  Your gun-fu is to be commended, I would've been looking for the Q-Tip end and when it wasn't found... probably buy a new carrier.

Hats off to ya

This occurance would not be a problem in in a gas piston upper design.  A gas piston design has no hole, no key for accepting gas, etc...  All the "ation" would be at the pistol and out of the way.  I have seen many incidents where the primer gets stuck within the hammer-trigger-disconnector area, the upper recesses of the upper reciever, and even get behind the firing pin.  With Mr. Murphy on the ever diligent prowl....

Quoted: Wow! That has gotta be a new one. Glad you found it.

Not really.  Carrier key is the common location where blown primers lodge themselves.  Not usually that far in, however.

Not a new one.  I personally witnessed this in a Colt Match HBAR several years ago and when I posted the story here, another AR owner chimed in with the same problem. It was damn hard to diagnose. We finally figured it out on the Colt when we shined a flashlight down the gas key and then decided to try and run a pipe cleaner through it. Blown primers end up in some wacky places....