but sometimes they arent? i have a set of dies that i used on some lake city match brass as well as on some commercial match brass, black hills and hornady. well the necks on the lake city will hold a bullet, the commercial neither will. the rounds can be pushed all the way in. lake city has thicker brass, commercial thinner. one works the other doesnt. so i gotta get a new die. but 308 is 308 right? so i score a deal on a PRS stock. i know, but i had a look in mind and this is what i wanted to build. well the guy had the tube, buffer and spring so i got them cheap. i take my 6 position off, put that on my 308 dpms and go to put the standard length tube on my ar15... threads line up, they are clean, i get 1 maybe 2 turns and it stops, its too tight to go in enought to retain the pin that retains the buffer. just cant believe the luck. ill try it in a few other lowers when my neighbor gets home. if i get ambitious ill try it in the 308. it came off a rifle so it has worked. ever have one of those days? lives? lol