I have a DPMS Classic A2 that came with their chromed carrier but with a parkerized bolt. Initially I had short-stroking issues, had to send it back to DPMS who "worked on the gas system". It seemed to function OK after that, but the brass was always going to 5 o'clock and into the next Zip code, which became a real problem at my range.
I noticed the cam pin metal was taking a real beating just under the cap, and began to suspect that the cam race in the carrier wasn't properly cut, since the bolt movement in the carrier did not seem fluid at all. I bought a parkerized carrier from Delton and used the original bolt, and that seemed to do the trick. Brass now ejects anywhere from 2 to 3 o'clock, depending on how hot the ammo is (mil vs commercial), the replacement carrier seems to move easier in the upper than the chromed one did, such as when manually locking the bolt back with the charging handle and bolt lock, and hand movement of the bolt back and forth inside the carrier is much smoother.
It's possible the chromed carrier was both slightly overspec due to the plating and had a rough cam race cut, both of which may have slowed the bolt timing down and caused my original short stroking. I never went back to DPMS about it, just happy to have it functioning well, and I keep the chromed carrier as a backup, since I know the rifle will function with it.