Reader submission: “Here in Brazil there are many laws that prevent us from carrying a weapon legally, but since nothing in Brazil works, we make our own weapons by hand. This is a .22 caliber made by members of a gang of punks here in my town.” The ammunition also appears to be improvised by inserting a lead bullet into a .22 blank round.
A quick and dirty improvised firearm assembled using pipe fittings available at any hardware store. Ammunition in this case has been improvised using nail gun charges with the crimp removed and a lead projectile inserted. The weapon functions by pulling back the ball end of the spring loaded striker bar and releasing to fire.
Two types of simple homemade open-bolt pistol designs chambered in .22lr. Those pictured in the first example have a conventional trigger while the examples in the second picture are fired by flicking the cocking handle free of a slot holding both it and the bolt back.