Bad day on the range this morning. I have a post Bushy 20" HBAR. I have put around 600 rounds through it with no problems. Mostly Q3131. I fanatically clean after each shoot. Maybe a little much on CLP but there is no dirt.

This morning I fired about 10 shots and all of a sudden it double fed and ended up with a live round with the butt end of the cartridge jammed up over the top of the bolt carrier between the carrier and the inside top of the upper. The bolt was jammed back about 1/2way. Pulling back on the charger only scooted the carrier and cartridge back and forward. I eventually got the cartridge out by pushing the carrier back through the ejection port.

After that, it would feed a first round but wouldn't extract. Sometimes the bolt would pull all the way back to extract, but it wouldn't go back far enough to chamber the next round. Other times, it would only extract the spent round about 1/2way out of the barrel. This was the most frequent jam.

I disassembled the bolt and thoroughly cleaned/oiled the upper, but it keeps doing the same thing.

The catch is... I switched over to feeding some brand new PMC so I don't think it is the ammo.

Could you have damaged the gas tube?  If your catridge was jammed above the carrier into the upper part of the receiver, it sounds like that is exactly where the gast tube is located.  Check to make sure it is not bent, crushed, and feeds into the carrier key, without binding.  Also, check you carrier key to make sure there is nothing obstructing this hole.  some use a pipe cleaner for this.

I don't think it was that far back on the bolt. The cartridge rim was caught between the extractor 'fins' on the bolt. It visually looks in good shape. I am going to take the entire gun down to check it over again.

Well, I dont think you would have damaged the key, but I am talking about the 1" or so of lightweight tubing that sticks out from the barrel into the upper receiver.

I would examine the extractor and the itty-bitty spring and the rubber deally on the bolt.  Does the extractor have alot of junk on it, so that the extractor won't snap over the extractor groove? I normally carry some spare parts like this in the pistol grip, so that if there is a problem extracting, I can them immediately.

Made a pic of the jam (I didn't have a cam on the range today).

Quoted: Well, I dont think you would have damaged the key, but I am talking about the 1" or so of lightweight tubing that sticks out from the barrel into the upper receiver.

I'd listen to this advice.  The gas tube that comes from the gas block on the front of the barrel runs under the handguard and through the front of the reciever just above the barrel nut.  It sticks into the inside of the reciever about 1" where in mates into the female gas baffle on top of the bolt.  Your double feed jammed exactly where that thin wall tube (about 3/16" diameter) ends before it mates with the gas baffle and may have bent/crimped/split it, allowing enough gas to escape to preclude bolt function.  Check it and let us know, I'm interested in the answer.  Of course, the fix is a new (and relatively cheap) gas tube.

shooter

Quoted: Made a pic of the jam (I didn't have a cam on the range today). http://www.accessconnex.com/jammedbolt.gif

Personally I have never had one jam on top like that. Is the one on top a live round. If it is it sounds like your mag might be letting go to soon. I have a CAR-15 it hates Q3131 and pmc, jams almost every round. There is a update of a little rubber washer that fits under the extractor spring that helped me a lot. Mine has a match chamber so almost all surplus is too hot and sticks in chamber. I could have ten jams in a row, then throw in old faithful(remington UMC) and runs all day long. Even after submerged in creek with mud and sand on it. Hope I could help. Doug

Shut up, go back and read warlord's post again.

This may sound stupid, but could the bolt be in the carrier backwards?

i was thinking the same thing. i did that once, felt so stupid. took out the bolt carrier, looked, the ejector facing the wrong side.

I had a jam like that once.  I cleared it and every thing was OK, for a while.  The gun would extract the round, but it would not pick up the next round from the mag.  It would do this about 30% of the time.  The problem turned out to be a damaged bolt carrier, more specifically, the carrier key was loose.  It turns out that one of the screws was stripped or broke.  I ended up with a new bolt carrier and everything is now fine.  This was on a Colt.

maccloud was the winner. Carrier key was loose but not damaged. i have not shot it yet to confirm but as loose as it was, I suspect this would have allowed enough gas to escape and not blow back the bolt far enough.