MACHINE GUN: This is a cool KICK-BUTT gun that only uses 4 pieces: black stud , black loudhailer , technic rod with stud , and a technic cog.
TOMMY GUN (MODERN) : Very simple , a long rifle , a claw , and a technic black cog/wheel. Stick the claw in the cog/wheel , the clip it onto the long rifle. Put the wheel and claw on the top of the gun to make a paintball-gun.
OLD-TIMEY PIRATE RIFLE: Only 2 pieces per gun. First , get a revolver and turn it upside-down and put a dark grey technic pin on the part the minifigure usually holds. The minifigure can hold above the little thing sticking out.
FLAMETHROWER: You need a scuba mask , a black visor , and a harpoon gun. All but the visor are included in the ocean speeder (Atlantis). Put the visor on the scuba mask and it looks like the gas-filled backpack that makes the fire. It also makes a fire-proof mask.