How can they know?
Start with the head stamp. If manufacturer didn't ship to CA in that year, you are out of luck.
If you buy boxes of 20 (rifle) or 50 (pistol), there is a lot number on the box. There is a lot of information behind that lot number. Including where the manufacturer shipped the product.
Wait...
Is it going to be illegal to buy ammo out of state? I thought the law only applied to shipping ammo into the sate. Ithought it was still legal to go out of sate, purchase ammo, and bring it home into Caliornia?
How canCalifornia do that? Doesn’t that violate the constiutionally protected Federal laws allowing intersate commerce. I mean, I can even buy guns out of state as long as I have a California FFL dealer transfer them.
There is no way we are prohibited from buying out of state ammo and atill allowed to buy guns out of state.
I don’t buy it that out of state ammo sales are illegal. I think the prohibition is only on shipping ammo in from out of state. I am sure you can still walk i in.