I have a new PCC build: Foxtrot Mike (FM) upper and lower kit with 15" handguard, 2-stage nickel boron coated trigger kit, FM buffer tube, heavy buffer and spring, Shooting Innovations 16" ramped barrel and bolt. Using only factory Glock mags and firing only factory Fiocci FMJ 124-gr rounds (PF 140). The gun functions perfectly, except after 150-200 rounds firing without cleaning, the gun pretty consistently fails to lock back. After detail stripping and, thorough cleaning, it again functions perfectly but then starts to fail to lock back. Can't figure this out. Any help from experienced Forum members? TIA