My understanding is, as a California resident, if you buy ammo out of state and bring it back across the California border it is a felony.
That seems to be accurate. I have a lifetime supply of lead hunting ammo, which is no longer allowed for hunting anything in CA, so most of my hunting is done elsewhere, except for waterfowl. And I have an adequate supply of non-tox for ducks, geese and the occasional pheasant hunt. When i go over the border to hunt, i take pics of all the ammo that's leaving CA, with GPS coordinates to prove it was mine when I left CA. And I have half a dozen loading presses in case any more fecal matter hits the fan around here.
And for those of you who may not be aware, all ammo transactions (including gifts), must go thru an FFL or a store with an ammo license (expensive), and the purchaser must pass a background check (with an additional fee). Even if you are buying a gun at the same time, with a background check and ten-day waiting period, there is a separate background check for your ammo. And the last couple of times i had ammo shipped to an FFL for transfer, they told me they were required to open the factory sealed flats and then open each individual box to ensure the ammo is as marked on the box. For that, they wanted to charge an additional $1 per box. Was told this by two different FFLs, so I stopped buying ammo, except for some speciality stuff before the excise kicked in.
Could it get any more ridiculous? The bastards will find a way.