I installed a 16" mid length barrel (with M-4 ramps). When I checked for alignment of the barrel extension ramps and the upper cut outs, I noticed there weren't any. I guess I grabbed the wrong upper.
It's got about 100 trouble free rounds through it, and I'm not seeing any scraping on the finish of the rifle upper from the cartridges feeding.
Should I change the upper out for one with M-4 extensions, or am I good to go?