My buddy has just bought a brand new DCM upper with SS barrel. He has been shooting Winchester 55 gr FMJ (US made) out of this upper. He was having FTF when the bolt would slam on the side of the fresh round on its way up into the battery. The casing was dented on the side. Short stroking? The empty brass was extracted and ejected OK. But upon closer inspection, I found some extractor mark on the case rim indicative of "hard extraction". I would not be surprised if someday the rifle will faill to extract the empty case from the chamber and the case rim will be torn off.
Since I was the one recommending him to get DPMS upper & lower, I would like to find out if there is something wrong with the upper, or is it the Winchester ammo that is out of spec (hard to believe since it is a commercial US manufactured ammo).
What are the possibilities here? Rough chamber? Out of spec ammo ? Or simply excessively tight cut chamber? Do we need to send the upper back to DPMS?
The gas key is tight and the upper was broken in per DPMS instruction. Adequate lubrication was added to the bolt and carrier.