With very few exceptions, California doesn’t grandfather equipment into new gun regulations. The presumption is if you possess ammunition/guns that aren’t on prior sale records (IE: out of state purchase), you need to declare and possibly surrender them.

Given that all in-state transactions are recorded (as I mentioned in my prior comment), if any LEO found ammo or guns in your car trunk along a state line, you’re cooked.

Not guaranteed to happen, but certainly not risk free.