These were found today in Argentina, used to steal cars and sometimes sold to other criminals. Pretty simple really, two metal pipes, one slightly larger than the other. A cap with a striking pin is screwed or soldered to the bottom of the larger pipe. Put the cartridge or shotgun shell in one, and slam it to the bottom of the other to fire the gun. When the smaller diameter tube, holding the round of ammunition hits the bottom of the larger diameter tube, the gun fires. When using a shotshell there’s no rifling left, and of course the “gun” being a couple simple pipes its very easy to hide or dispose of.
Now, if you want to see an incredible gun made with scrap steel, a drill and grinder check the video below! By the accent, the person is from Cordoba, Argentina.