Ammo Pistol is a term used to describe four different types of firearms: CAPS (4 letters), CAP (3 letters), PEA (3 letters), and STEN (4 letters). CAPS stands for Colt Automatic Pistol, which is a semi-automatic pistol manufactured by Colt's Manufacturing Company. CAP stands for Colt Automatic Pistol, Small Frame, which is a smaller version of the Colt Automatic Pistol. PEA stands for Pistole Parabellum, which is a semi-automatic pistol designed by Georg Luger and manufactured by German arms manufacturer Deutsche Waffen- und Munitionsfabriken. Finally, STEN stands for Short Tank Enfield, which is a British submachine gun developed during World War II.