It was common practice in the late nineteenth century for cowboys to carry a rifle and a pistol chambered in the same caliber. This made sense from a practical point of view: if your rifle and your pistol used the same type of ammunition, then you only had to carry that type, and your preparation

The MP5 originated as Heckler and Koch’s Project 65. It was created as a roller delayed blowback evolutionary descendant of the revolutionary MG42, which featured the first mass produced roller lock mechanisms and stamped metal firearms technology. There were a number of successful submachineguns already on the market, with the Uzi being the most ubiquitous