I have a situation I am unable to diagnose on a new build. I have a new lower pistol build and I am attempting to attach an upper. The upper fails basic function testing. I can't pull the charging handle all the way back without forcing it. If I pull past the point of resistance then the BCG gets stuck and doesn't return forward. I have to use the forward assist to send the BCG back into battery. When I try the same upper on another lower, everything works fine. When I try a known good upper on the problem lower, I experience the same issue. So the issue is definitely with the new lower. Any ideas? I don't see any new wear patterns or drag marks on anything. Any ideas on where I can start troubleshooting? I'm kind of stumped.
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