I just finished assembling a 16" DPMS kit on a DPMS lower. Parts all looked pretty good (except the weid handguards), but it won't chamber a round properly. Once a round is fully or partially chambered, it becomes very difficult to extract. There are small scratches on the case and a single deep gouge in the bullet (consistent for all seven rounds chambered and ejected.) I've shined a light into the chamber and down from the muzzle and cannot see any visible burrs. I tried cleaning the barrel well in case it was just some abrasive junk, but that didn't help. Obviously I did not want to fire it like this, so I'm probably going to end up sending the upper back to DPMS for them to fix. Anybody had similar problems? What'd you do to fix it? I hate to ship it back for repair after just finishing it, but I reckon that's what I'll end up doing.

Me -> advanced noob.

If it is chromed plated, they need to replace the barrel,
If it is steel, it can be redrilled/reamed to proper dimentions.  

If it is new, just send it back..

Edit.. hows headspace?

Yeah, I should've mentioned that. It's a stainless barrel, not chromed.

Can't be sure of headspace-- haven't checked it. Figured with it having that much trouble chambering/extracting, headspacing would be putting the cart before the horse.