If someone were to ask you, "What is the single, most unique part of a revolver?" you would have to answer "the cylinder". The cylinder is associated with all revolvers because it is the most unique part of the gun, a part which will not be found on any other pistol model. The cylinder is mounted behind the rear of the barrel and holds ammunition designed specifically for that gun. The cylinder is different from the semi-automatic pistol in the fact it holds ammunition that will send the bullet down the barrel. A semi-automatic pistol "chamber" is a widened section of the barrel that accepts ammunition which is placed into the barrel section. A revolver does not place ammunition into the barrel, therefore, the "chamber" is the "cylinder" which holds the ammunition. The cylinder rotates in a circular fashion and holds a varying amount ammunition, depending on its caliber. The design of having the chamber separate from the barrel creates a unique gap between the cylinder and the barrel known as the barrel-cylinder gap. This gap, which is typically between 0.004" and .008" allows the cylinder to rotate freely. While some gasses escape through the gap, it is not sufficient enough to lower the velocity of the bullet, however, it is sufficient enough to be seen and heard. Always keep the barrel-cylinder gap free from obstruction, especial your fingers or other body parts as the gasses are hot chemicals that can cause injury.
The "original", "grass-roots" cylinder gun rotated a set of barrels where the ammunition was loaded into the barrel chambers. As the chambers rotated, they came into a firing position, making the revolver of those day's an advanced weapon. The ability to fire successive shots without having to reload was an everyday miracle. The firearms were termed "pepperbox" firearms because they could deliver more than one round in succession.
There are two basic types of revolver pistols: Single action and double action. The single action revolver is an older style revolver and seldom manufactured in today's modern firearms plant.
The single action revolver requires the user to "cock" the hammer manually, which rotates the cylinder and loads a fresh round of ammunition behind the barrel. In the older "cowboy days" this was the pistol they needed to contend with--draw, cock, fire, cock, fire, cock, fire. In today's modern world of self defense tactics, drawing, cocking, firing, and then cocking again is an unrealistic proposal for personal self defense.
Before we move on to the more popular "double action" pistol, we need to understand the operations of the single action pistol.
The Single Action Pistol
To operate the single-action pistol, the hammer must be cocked first which places pressure in the main spring and retracts the bolt or cylinder stop out of engagement with one of the notches in the cylinder, allowing the cylinder to rotate freely.
As the hammer is drawn rearward, the pawl or hand, which is attached to the hammer, moves vertically in a slot located in the recoil shield portion of the frame. This engages an offset ratchet on the back side of the cylinder which produces the rotating action.
The ratchet and the pawl are carefully designed to align the chamber with the bore of the barrel after the hammer has been completely cocked.The cylinder bolt (or stop) snaps into the next notch, securing the cylinder in the proper position. Once the pistol is fired, the process repeats.
Double Action Revolvers
Double action revolvers are named for their ability to cock the hammer and to fire the shot (release the hammer) in one pull of the trigger. The double-action mechanism that allows the revolver to work is made possible by adding a separate double-action sear on the hammer which is engaged during the pulling of the trigger. As the trigger is pulled back, the hammer travels into the firing position and is then released once the trigger passes the designed breaking or release point.
Double-Action Only Pistols
The long, heavy, deliberate pull of the revolver trigger has always been considered a safety feature in-and-of-itself as the chances for an unintentional discharge is extremely unlikely. Modern revolvers may or may not have additional safety features built into them which are not directly controlled by the gun owner but are disengaged when the trigger is properly pulled. Revolvers which have the firing pin as part of the hammer, have an additional safety feature which prevents the hammer from closing completely unless the trigger is pulled. Some manufacturers will include additional safety features the gun owner may choose to engage or disengage manually.
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Some double-action pistols are designed primarily for self-defense. These revolvers rely on the internal striker style mechanism. This style of revolver cannot be "cocked" in the same manner as the single or double-action revolver. The pistol is limited to the double-action only style of firing, hence the name of the triggering mechanism.