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.