Yo, fellow guardsman here. Answer to your question is no, I've already contacted the DOJ in regards to Active to Guardsman transitions. They won't allow it, but here's what you can do from my own experience, kinda mentioned above.
First, whatever base you're going to, try to establish an off base housing... whether it be your own or just a buddy's. If you're going to basic training, and then to Tech School/AIT (whatever branch you're in), you'll have to wait till schooling... impossible to do all this in basic! lol. Once in school, if you're married I know in the Air Force you can become SEP RAT and get off base housing once you've made Phase 2 (you'll understand what all this means once you get to that point). If not married, I'm sure one of your wingmen/battle buddies will be. Just use their address and your military ID to obtain a local state ID. From there, if you intend on bringing it home, just make sure the make and model is not on the banned list
ag.ca.gov/firearms/regs/aw.htm and that it doesn't have AW features as set in PC 12276, then you may bring it back with you to California.
A heads up while you're gone, if the firearm you purchased while TDY goes on to the ban list, be sure not to miss the registration period, or you're SOL! Also, especially if you're NPS, don't try and keep any kind of firearm on base, you're base commander will have a shit fit... with you right in the middle... I suggest leaving it at an off base location, like your buddies address you used. Have fun in the Guard!
Technowizard.
p.s. whats your unit? Just curious.