Quoted:
So, if I were to temporarily establish residency in a neighboring state, made my purchase, and officially moved back into CA without bringing the rifle in, that'd be legal? Would I still have title to it?
If you are a resident of ANY state (not necessarily neighboring) that allows sales without additional state bs, you can legally buy the rifle. Buying the gun will require a driver's license. Getting the license will usually require some kind of proof of residency...power bill, paycheck stub, passport, etc.
If you're thinking of dual residency, make sure you talk to a professional tax person, as there a lot of ramifications that affect your PRK state taxes (imagine that).
I'm not recommending or condoning anything, but if you even think you might move to the prk in the future, consider getting a duplicate copy of your current driver's license before you move. Give the old one to dmv in prk when you get a prk license.
-hanko