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.

The safety notch replaced pins on the rear of the percussion revolver cylinders, which served the same purpose as the safety position, by preventing hammer contact with the primer/percussion cap.
However, many users adopted the practice of leaving one empty chamber under the hammer, because a sharp blow could damage the mechanism and allow a fully loaded revolver to fire.
This practice is now universally recommended.
Drawn back about half way, the hammer engages the second notch.
This cams the cylinder bolt out of engagement and allows the cylinder to rotate for loading.
Fully cocked, the revolver is ready to fire.
Cartridge ejection is via the spring-loaded rod housed in a tube on the right side of the barrel.

The loading sequence is as follows:
Place the revolver on half-cock and open the loading gate to the side.

Load each chamber in sequence (original), setting the hammer in the safety notch when finished; or (safe and prudent method) load one chamber, skip the next, load the remaining four chambers, close the loading gate, draw the hammer to full cock and lower fully, making sure that the firing pin is over the empty chamber.

Firing the revolver is accomplished by drawing the hammer to full cock and pulling the trigger.
The hammer must be manually cocked for each shot.

It is possible to fire the SAA rapidly by holding down the trigger and "fanning" the hammer with the other hand.
Ed McGivern dispelled the myth of the inaccuracy of this procedure by shooting tight groups while fanning the revolver.
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. 
The safety notch replaced pins on the rear of the percussion revolver cylinders, which served the same purpose as the safety position, by preventing hammer contact with the primer/percussion cap. However, many users adopted the practice of leaving one empty chamber under the hammer, because a sharp blow could damage the mechanism and allow a fully loaded revolver to fire. This practice is now universally recommended. Drawn back about half way, the hammer engages the second notch. This cams the cylinder bolt out of engagement and allows the cylinder to rotate for loading. Fully cocked, the revolver is ready to fire. Cartridge ejection is via the spring-loaded rod housed in a tube on the right side of the barrel.
The loading sequence is as follows:
Place the revolver on half-cock and open the loading gate to the side.
Load each chamber in sequence (original), setting the hammer in the safety notch when finished; or (safe and prudent method) load one chamber, skip the next, load the remaining four chambers, close the loading gate, draw the hammer to full cock and lower fully, making sure that the firing pin is over the empty chamber.
Firing the revolver is accomplished by drawing the hammer to full cock and pulling the trigger. The hammer must be manually cocked for each shot.
It is possible to fire the SAA rapidly by holding down the trigger and "fanning" the hammer with the other hand. Ed McGivern dispelled the myth of the inaccuracy of this procedure by shooting tight groups while fanning the revolver.
Colt Single Action Army