re: PSA Pistol Upper

to use a personal example, i ordered and received a 10" barrel for my uzi, before my SBR stamp arrived. i was in violation of federal firearms law for the time i had the barrel in my possession without the stamp, because of the constructive possession clause, even if i never fit it to the firearm

now...under what circumstances would an ATF agent have come to my house, with a warrant, to search out and discover both the barrel and the firearm it could be mated to? i guess you could say probable cause would have been my purchase of the barrel, but thats a stretch

i'm not advocating anyone break the law, but like i said the chances of discovery are too small to compute