I'm in the middle of building another NM upper. I ordered a NM rear sight base from Brownells, a Prarie River Arms. When I received it I matched the base threads up to my CLE 1/4 MOA rear base. The threads didn't match up. I figured it was a 1/2 MOA base. I put a indicator on both bases. The 10 click average for the CLE was .019". The 10 click average for the PRA was .015".  One of these is not a true 1/4 MOA base.  The PRA is not 1/2 MOA. I measured a standard base and the 10 click average was .060".  What is the true movement of a rear base for a one inch shift in shot placement? Thanks.