Alright, so I'm currently working on getting a 9mm AR-15, and getting it registered so I can slap a 10.5 upper on it (because that's cool and stuff).

Thing is, I really only want one lower right now, and I travel to Alabama at least twice a year. Alabama would frown upon my little 634 clone.

So, could I take the 10.5 upper off and put the 16 incher back on and be okay in Alabama or any other non-NFA state?

I mean, Alabama doesn't prohibit SBR registered rifles in the law, just those rifles that have under a 16 inch barrel. If it didn't have the 10.5 inch on it (and that upper was still up here), would there be a problem?