IIRC, after exhaustive study, #4 shot is what the FBI settled on.
Of course, over penetration was a critical factor in their decision.
Edit: I just looked it up and # 4 birdshot is much smaller in diamter than the #4 buckshot that the FBI adopted. Sorry.
Proud NRA Benefactor Member
Last edited by Microgunner; January 20, 2013 at 04:53 PM.