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My first AR15 with a Bushmaster XM15-E2S. I wanted a flattop, so I bought a CMMG complete upper and did a switch with the original permanent-carry-handle (A2?) upper. Life is good for a year with my Bushy lower and CMMG upper - no problems.
Just before the election, I decided I wanted to get another lower to match with the complete CMMG upper, and put my original Bushmaster back together.
I bought a Rock River stripped lower (marked LAR-15 / 5.56cal) and a DPMS lower parts kit with a Tapco stock - took until today to get it all assembled. Everything went together ok, with the exception of the rear takedown pin being VERY tight - was not hard at all to get in into the lower, but once the rear takedown detent and spring were in place and the stock was tightened, it's VERY tough to push out the takedown pin.
That's bad, but what's worse (and the real reason for my post) is that neither my Bushmaster NOR my CMMG upper will match up with the now-assembled Rock River lower. The front pivot pin goes in fine, but when trying to "pivot the upper closed" the rear takedown catch on the upper seems not to want to "mate" with the Rock River lower. It simply won't close all the way - feels like the RR lower is too "short" by a millimeter or so to fit either of the uppers correctly.
Here's a picture of the CMMG upper and Rock River lower "about" to close - you can see the wear marks (circled) where the upper and lower rub when I try to pivot the upper into the lower. In this picture, I've also removed the buffer/buffer spring, and the bolt carrier group, just to eliminate those as problems. The same issue happens with those parts in place.
Help! Any ideas?
