I see that most manufacturers sell uppers either with or without a bolt assembly. As far as headspace is concerned, can I swap an upper and use the bolt in my orginal rifle? If I can, then that would mean that head space is done without a bolt. In another words to keep proper headpsace, the bolt and barrel do not need to be matched like most other semi auto designs and bolt action rifles. Am I right? This seems like a simple question, but I can't find and answer to it anywhere?
Also, when the AWB sunset occured, I had my post ban barrel threaded and A2 FS put on it. To do so, I presume the shop had to remove the barrel from the upper to turn it to thread it. When they put the barrel back on, they did not have my bolt. (I just gave the shop my upper with no bolt or lower.) Would that matter? Could the headspce be correct if the shop did not have my bolt? How could they check headspace without the bolt? HELP!!!