The firing pin is a small, pointed, metal rod which is eiter struck by a hammer or is spring-loaded and held in place by a shear in the bolt or firing pin block. When released, or struck, the rod moves forward and strikes the primer of the ammunition in the chamber of the firearm, firing the round. It has been common to see firing pins in rifles since the late 19th century and they have seen growing popularity in pistols since the late 20th century, mostly made popular by Glock. They have also been implemented on revolvers so that carrying with an empty chamber is no longer neccessary.