Regarding a TRUE M4 carbine- they are select fire (tri-burst) and NOT transferrable to a private citizen. They were not made until AFTER the cutoff date for registration of full auto firearms (May 1986).
You could have something that LOOKS like an M4- you could have an M4 upper on a full auto lower that was registered before the end date- but you will not have a true M4.
This is what I thought to be true regarding an M4. Please everyone go back and read my OP. Not MY son, the son of a guy I work with. I have stated all of the info I have, will inquire further Monday. I do not believe we are talking about a full auto firearm, though, or even an SBR. Also, as far as I'm aware, you do not get to receive or put together an SBR or full auto and THEN transfer it, or get the stamp, that has to be done 1st.....
BTW, in NH, we are allowed to have pretty much anything the Feds say we can have. NH is a very non-restrictive state. Mass. makes up for it. I am also wondering if there are any anti-gun groups that are sending letters hoping to screw with people, and collect/get them to give up info......