Sent the upper back due to a rough chamber and had it polished.  According to DPMS (email today) the chamber is 5.56 even though the barrel is marked .223 and "is fine to fire with surplus ammo".

I fire appx. 10-15 rounds mil. surplus, then either the bolt fails to pick up the next round or the fired brass is half-way out of the chamber and the bolt half-way open.  

I'm stumped.  After the first 10-15 rounds, it becomes a single-shot.  

Suggestions (other than getting rid of it, which I may do anyway).

Thanks.

saw another AR doing this.  it sounds like it could be a gas problem - port not clear w/ some burr blocking it, possibly.  that would take removing the front sight and de-burring it, preferably done by a competent AR smith.  another thing would be to check the carrier key on top of the bolt carrier.  mine worked loose and dinged up the end of the gas tube one shooting session.  never had a problem til then.  also check to insure you have a good lubed carrier and bolt.  running one dry in the upper can mess up the feeding as it doesn't always cycle back smoothly and all the way - shortstroking.    

Sounds like you're losing gas somewhere.

My DPMS was doing the same thing. It would shoot, then the bolt would only go back about half way through the ejection port and stop. I had Dano polish my chamber and now it ejects everytime. I have other problems with it not jacking in a new round but that is a whole different story.

You guys checked to see that your gas key on your bolt carrier is locked down tight?

Yeah, the key is staked and tight. There is no gas leak either. Mine was a rough chamber which cause the shell to stick after expanding from firing. Dano who posts here polished that baby like a mirror. He knows his AR's. Mine jamming up on the forward cycle is due to hammer issues it sounds like.

Thanks for the help.  I'll try once more with it and see if polishing the chamber helps, it seems to shoot fine when clean, then after 10-15 rounds, when deposits start building up, the problems start.  There appears to be carbon on the gas tube just behind the front sight under the handguard for about 1".

Had the same problem with my j&t kit, they told me to clean it with a chamber brush, I attacked the thing over a period of 3 days until my arms hurt with a chamber brush and still no luck, sent it back yesterday.