I was testing a new USGI 30rd yesterday. The first 3 shots went off without a hitch and then I started having problems; a failure to extract on every subsequent round. Just to rule out a mag problem (which I knew probablyt wasn't to blame) I tried two others including the factory 10rd mag from Bushmaster; same thing. When I got home and tore it apart everything seemed visually correct. The extractor and ejector and their respective springs/pins were all in working order. The gas rings were fine; everything "looked" fine. I thought "well what the heck?". I inserted an Alan wrench into the hex nuts on the carrier key to remove it; the nuts turned very easy and weren't tightened down all the way. Right away I knew that was the problem. Enough gas was escaping between the key and the bolt carrier so that there wasn't enough pressure to push the carrier all the way rearward. I knew this because the necks of the spent shells weren't even clearing the chamber on their way out the door; they weyre staying in the bore! I assembled everything and ran 30rds thru it without a problem. Just goes to show how absolutely crucial a role each little part of this rifle plays.  

Any difference in accuracy from the non-clearing rounds?

Not an expert here, but....

Those screws need to be staked, otherwise they will back off again and can cause a weapon malfunction. Can't remember if it can cause damage. Check with the maintainence forum for details.

YMMV
M4-AK

No difference in accuracy. Now what's the difference in "staking" the screws and tightening them down? If there's a difference how do I stake them? Sounds important.

You may have damaged/weakened the the carrier key hex screws by firing the rifle with them loose.  I would suggest replacing the hex screws and staking them in place AFTER they have been torqued to specification.  I would not want the screws to shear and have the key get jammed (or worse) in the upper receiver.  Staking is a process using a heavy hammer and a hardened steele punch to create a dimple in the carrier key near the hex screws.  These dimples bind up the head of the hex screws and prevent them from backing out.

Quoted: You may have damaged/weakened the the carrier key hex screws by firing the rifle with them loose.  I would suggest replacing the hex screws and staking them in place AFTER they have been torqued to specification.  I would not want the screws to shear and have the key get jammed (or worse) in the upper receiver.  Staking is a process using a heavy hammer and a hardened steele punch to create a dimple in the carrier key near the hex screws.  These dimples bind up the head of the hex screws and prevent them from backing out.

IMO, If you use a "heavy hammer", you may damage the key beyond repair. You just need to "squeeze" the metal into the screw heads. AB

Torque them down, then dimple the metal on the gas key on the right and left side of each screw head.

Thus, you will have 4 crimpings that will not allow the screw heads to turn.

get ahold of someone with a COLT Bolt carrier to see what it should look like.  Its not a hard job to do yourself if you have a bench vise.

This is so funny. It seems alot of us are having this issue all of sudden.

Please refer to my posts here for more info.

http://www.ar15.com/forums/topic.html?id=123300

And here too

http://www.ar15.com/forums/topic.html?id=123302

Quoted: This is so funny. It seems alot of us are having this issue all of sudden. Please refer to my posts here for more info. http://www.ar15.com/forums/topic.html?id=123300 And here too http://www.ar15.com/forums/topic.html?id=123302

Yeah, check out the troubleshooting and maintenance sections. We have about 3 topics in each! I'm still looking for a 3/32nd inch hex bit for a torque wrench.

Yea that tools a tough one.

The key didn't come staked from the factory? My Colt did.

I think I've read enough about the Bushmaster quality control problems to at least raise my level of skepticism.  

It should be an easy matter to contact Bushmaster, explain the problem, have them issue a UPS pickup and send the bolt carrier back to them for proper repair.  I've read of their prompt customer service.  Why don't you fellows let them handle it under the warranty?