Short stroking: here is my recent experience on a new lightweight build. Aero upper, McKay Industries lower, solid quality lower parts, to include Geissele trigger. Bolt carrier group from X, stock/buffer/buffer tube from Y. You would easily recognize X and Y, not bargain basement. Ballistic Advantage Hanson barrel, which I first suspected as the culprit.
Solution: I thoroughly cleaned everything. I replaced X BCG with a new Toolcraft I had laying around, and replaced buffer and spring with one from known Colt factory lower. 200 rounds later, not a single failure with IMI M193 and old Colt 20-rounders. Lubed with Mobil 0-20 synthetic.
I realize this is not following the scientific method, but I just wanted to shoot the rifle. Later, I'll swap parts to find the offender. I noted buffer from Y had no marking on it; Colt buffer clearly marked "H". Buffer springs had same number of coils, but one from Y was over two inches longer. Go figure.