What sort of gun would you want? At the age of 17 I owned an SKS with folding stock, 30 round mag and bayonet: Right now, in every state but California, you can run out and buy a .50 BMG sniper rifle with 8 round mag: (AKA the "Cobra Assault Cannon" from Robocop) How 'bout an HK91 with drum mag? .308 which means it'll go through most any body armor: If you really want "deterrence" I recommend the Lahti 20mm anti-tank rifle: (fun fact: When the Finnish used these against the USSR in the Winter War, they supplied this "rifle" with a trailer to tow behind jeeps) Then again, all this stuff requires aiming. Sometimes you just don't have time for that. That's when you need an Armsel Striker: And hey, if that's not enough for you, sign up for a Class III NFA. Then things start getting really silly:
