01-24-2016, 04:17 PM
I have built about 20 AR's of various persuasions and started lapping after one of 'em was sufficiently off-square that I could see the barrel angle. Most have been"pretty close" but none have been truely square. Also note that I will only use forged uppers.
There is another consideration, I picked up some ceracoated uppers with the coating applied to all external AND internal surfaces. When I did a first pass "do the pieces all fit?" there was some interference between the bolt and the coating inside the upper. Using the rubbing compound with the tool on both the length of the tool shaft and the barrel mating flange it cleaned it up real well. Note, when doing this, I mount the upper in a vice vertically so that there is no lateral force to the process.
There is another consideration, I picked up some ceracoated uppers with the coating applied to all external AND internal surfaces. When I did a first pass "do the pieces all fit?" there was some interference between the bolt and the coating inside the upper. Using the rubbing compound with the tool on both the length of the tool shaft and the barrel mating flange it cleaned it up real well. Note, when doing this, I mount the upper in a vice vertically so that there is no lateral force to the process.