A zip-gun designed by the inmate of a midwestern State penitentiary (Cincinnati) was constructed in the prison machine shop from a piece of pipe in which springs had been inserted and a trigger affixed. The gun operates when the rods used as projectiles are inserted into the pipe, the springs are compressed and held in that position, and the trigger is pulled.
The designer and maker of the weapon had meant to use it against a fellow inmate, but when he fired it, the projectile missed its intended target. The gun was confiscated and obtained from the penitentiary during an investigation by the State highway patrol.
Federal Bureau of Investigation
<a rel="nofollow" class="external text" href="https://leb.fbi.gov/file-repository/archives/november-1966.pdf">FBI Law Enforcement Bulletin</a>, November 1966, Vol. 35, Number 11, Page 19