How does State to State transfer work

[coyote43g]

My brother, who lived in Massachusetts now resides in the state of South Carolina. While still living in MA, he bought himself an M1A scout rifle that was deemed MA legal. Now, he wants to just out right give me the rifle since he no longer wants it. Our best bet is transferring it via FFL and we know the fees are applied. Is there anything else that my brother and I need to know? Are there any modification differences between the MA legal M1A with the CA legal MIA? Thank you for reading and any response would be appreciated.