4 bore.. what is that 4 inch" ? You're f'ing nuts!
Hell my Uncle used to have an 8 guage and that was big!!!! He never even shot it because the guy he bought it from (a HUGE dude) said it kicked like getting hit with a truck.
Anyways.. good luck with your project
PS - How much of a pia is it to bring pistols into NY and register them... just wondering. I'm in PA if it helps.