My situation, i own a complete Stag .223/5.56 2tl and am (interested)in the process of building my own SBR and would like to go 300
AAC. Again, I own a complete 16" rifle and have just purchased the left hand upper and BCG from Stag for the build. I started there only because of the availability of the parts, left hand stuff can be tougher to find at retail price. I want the Noveske 8.2" 300 barrel and would like to start watching for it at a reasonable price because they aren't all that common. I'm not in a hurry to complete this and I have NOT applied for the tax stamp yet.
How far can I go with collecting parts before I am legally crossing the line? Does owning(and storing in the same location) a complete rifle complicate the situation? I would prefer to retain my current firearm possession status and keep my ass out of jail

Thanks!