Bloke goes into a gun shop, and asks for a gun, the gunsmith asks "whats it for mate?" and the bloke says, "Oh, its just for shooting some cans in my garden".
The gunsmith says "ok, you can have a small rifle for just shooting cans", the next day the bloke returns to the shop and asks for a machine gun, the gunsmith says "bloody hell, what sort of cans are you shooting at?" and the bloke says "Oh, Americans, Africans, Jamaicans and Mexicans"