Took my new DPMS carbine to the range for the first time today.  I inserted a fully loaded 30rd magazine, pulled the charging handle, fired and the gun failed to extract.  I cleared the jam and fired the next 29 without a problem.  This happened twice more using the same magazine.  I know 90 rounds isn't much of a break-in and problem will probably go away by itself after more rounds are fired, but I was wondering if this is typical with a new rifle and whether this is why some people suggest loading magazines with one less than full capacity.  

The gun is tack driver by the way - one ragged hole at 50 yards.

what ammo were you using?

60 rounds of Malyasian surplus [brass cased] and 30 rounds of Winchester white box - ammo was not mixed in the magazines.

It's normal but the rifle should work out of the box capisce'?

An overloaded mag won't, commonly, cause failures to extract. Failures to feed, failure to lock yes, but not FtEx.

DLing is recommended, not by me, to simplify reloading the piece. With the reduced tension offered by the one less round the magazine will seat easier.

If it's new send it back to DPMS. Or, get a stiffer extractor spring and swap it into the piece.

Since the problem is mag related, with the problem being that the mag/follower is having problems being able to allow the carrier to force the 29 loaded rounds back down into the mag to allow the carrier to move back over the top round on ejection, my vote is to pull the Mag apart, clean it, knock the plastic burs off the followers sides, lightly lube the inside of the mag body, the spring, and the follower and then re-assemble the mag.
(taken big breath after that long of a run on sentence).  

Also, if needed, you may have to tweak the mag feed lips at the middle. Sometimes the lips (center of body) flair out, and the top round can be jammed into the side of the mag, just above the top of rib, instead of being push down into the main body of the mag. The fact that it only happen at the 29 round mark may just be spring tension/ follower binding point.

Once the mag has broken in (read self polished), pull it apart and run it dry
(added to appeal to the guys that demand that the mags be run dry).

Note: All factory GI mags come with grease inside of the mag (globed to the spring). This to add the mag until it polishes it's self out the inside of the body and self-grind/knock the followers burs off.  The problem is that most new mags on the market have been sitting for a long time, and the grease has turned into a hardened state, or the used mag been re-finished or solvent tank cleaned (with new green follower added) without re-applying the grease.

P.S. The area/item question that seemed to be missed is this only happening with a single mag or a group of mags, and is/are the mag(s) USGI.