Which Firearm Design Is Uniquely American?

Which Firearm Design is Uniquely American?

Over-under Shotgun
Over-under shotgun
Semi-automatic Pistol
Semi-automatic pistol
Flintlock Pistol
Flintlock pistol
Bolt-action Rifle
Bolt-Action rifle
Lever-action Rifle
Lever Action rifle
Double Action revolver
Double Action revolver