The Colt model 1903 pocket hammer is based of of the 1902 sporting model, which is in turn a civilian market variant of the Colt 1900. Like it's immediate forerunners it is a .38acp chambering, of course not to be confused with the later .38 Super, more on that later. It's a locked breech design featuring a swinging link much like the 1911. However unlike its progeny this pistol is blessed with dual swinging links; one at the rear of the barrel and the other at the front. Another noticeable difference of this earlier design family is the lack of a barrel bushing, rather the front of the barrel is flared in such a way that as the slide returns to battery it forces the barrel forward and back up into it's locking notches; not unlike certain sub-compact models of the 1911 today.