I was thinking about building my own upper, but was strongly advised by the MFG tech support unless I had a what he called a special "Jig" that has "Spines" that looks like a bolt carrier, but what that allows is to achieve proper alignment and torque of the barrel nut.

He said if you were to build this using the conventional means, "home methods" that there is a chance I may or may not get the indexing right on the first try, and that you can only loosen and re-tighten the threads on the receiver before they become basically no good.

I am now scared to try and build an upper because it seems too hard. Is what he is saying about loosening and re-tightening the barrel nut will ruin the threads? He said maximum 2x maybe 4x most.