I’m not an attorney, but I beleive it is a simple tenet of law that “ignorance is no excuse.” That would make both parties responsible for violations of a law involving the transfer of “contraband.” that doesn’t mean that in the case of police intervention, that both parties would be charged. that would, I assume, be subject to a review of all the circumstances. If both parties were in California, with the transfer taking place in California, both would be charged unless there was excusable ignorance (like a little old lady widow giving away an illegal war souvenir item brought home by here husband. I don’t think that even in a state like California, such a party would be charged in that no one could expect her to know the laws on ammunition - however, the person receiving the ammo, if a person who should know, like a dealer or arms collector, would probably be charged.
Of course, not a simple question to answer, I suppose even for an attorney. I have some background in firearms law as we had to be aware of the laws as professional dealers, but again, I am surely no attorney, and do not have an attornies background in legal interpretation.
I can’t speak for other states - have never lived anywhere but California and Alaska, and at the time I was in Alaska, it was a Territory, not a State.