the laws get real fuzzy with regards to SBRs.
now before you jump all over me, hear me out.
i have a coupla SBR ARs, so for those 2 registered lowers i have 3 shorty uppers to swap out. along with the SBRs i also have a RR M-16 that legally can use whatever length upper.
now, i ALSO have title 1 ARs.
see where i'm going with this? it gets fuzzy, i say that because there have been arguments in the NFA forum here on the legality of owning extra uppers or extra M-16 FCGs while also owning title 1 ARs.
i don't know how many people have been put in the slammer over "constructive possession", but having a AK pistol laying around with a drilled out trunnion, and there, laying next to it is a stock that will screw right on, well that just aint smart.
otoh, if you have a rifle with that stock on it, along with an AK pistol in the safe, theres no problems.
besides, in a shtf situation, you do NOT want to be converting firearms.... now, in TEOTWAWKI, thats different!!!!!!!