half-cock

thumb|Colt Single Action Army hammer at half cock Half-cock is when the position of the hammer of a firearm is partially—but not completely—cocked. Many firearms, particularly older firearms, had a notch cut into the hammer allowing half-cock, as this position would neither allow the gun to fire nor permit the hammer-mounted firing pin to rest on a live percussion cap or cartridge. The purpose of the half-cock position has variously been used either for loading a firearm, as a quasi-safety mechanism, or for both reasons. The still commonly used English expression of "going off half-cocked" derives from failing to complete the cocking action, leading to the weapon being unable to fire. This is often used to describe someone acting prematurely, as in the case of one preparing to shoot their weapon without having set the firearm into "full-cock" position.

== Early examples == thumb|Cutaway view of the action of the Remington-Ryder No. 22 breech-loading rifle, which loads only with the hammer at half cock. Figure 1: Arm at the moment of discharge. Figure 2: Open to receive the cartridge. Figure 3: At half cock, loaded. Early flintlocks had required a half-cock position to prime the pan, in preparation for firing the firearm, after loading the main chamber. Some other early types of revolvers, such as the Colt 1851 Navy Revolver, required the user to place the hammer at half-cock to permit rotation of the cylinder to load the firearm. On such firearms, the standard practice was not to load all 6 chambers and leave the hammer at half-cock, but, rather, to load only 5 of 6 chambers by standard safety practice, and stow the dropped hammer on an unloaded chamber. Nonetheless, some users did use the half-cock notch as a very early safety on such revolvers when all 6 chambers were loaded, often to a dangerous and unintended consequence.