The Single Action Army action is a refinement of the earlier Colt percussion revolvers and the Colt 1871 cartridge revolver. The cylinder is mounted on a central axis and operated by a hand with a double finger whose more extended action allowed the cylinder-ratchet to be cut in a larger circle, giving more torsional force to the cylinder. Four notches on the face of the hammer engage the sear portion of the trigger, affording five basic hammer positions. The hammer when fully lowered rests within the frame. Drawn slightly to the rear, the hammer engages the safety notch of the sear and holds the firing pin out of direct contact with a chambered cartridge. Like the earlier percussion revolvers, the Single Action Army was designed to allow loading of all of the chambers.