It depends on how you define a "crime" with a machine gun. If you define a "crime" to be mere possession when the government says the possessor shouldn't have the machine gun, then there'll be quite a few. If you mean an illegally possessed machine gun that's used in a violent crime, then there'll be a lot less; not nearly as many as a lot of people would like you to believe. If you mean a legally possessed, privately owned machine gun that's used in a violent crime, then the number is in the single digits.