The early revolvers such as the first Colt Paterson models of 1836 had a very primitive reloading mechanism. As these revolvers were muzzle-loaders using percussion-cap technology, the user was required to disassemble the gun to reload it. The user would first put the hammer at half-cock, then open a latch in front and pull out the barrel and cylinder from the revolver frame. The user would then fill the cylinder's chambers with gunpowder and a ball in each chamber. Then the user would tamp each ball down with a ramrod. Then the user would assemble the gun back and then attach percussion caps to the back of each chamber. The small revolver on the picture above is a Colt 1836 model.
Obviously, such an operation took a long time. Hence, some people would walk around with already loaded spare cylinders in their pockets. That way, all they had to do was to pull out the barrel and cylinder from the revolver frame, substitute the new pre-loaded cylinder and reassemble the gun.
The Colt Paterson model of 1839 improved on this by putting a loading window on the side of the weapon, near the front of the cylinder. Colt also attached a ramrod on a hinge, on the underside of the barrel. Using this system, the user did not need to disassemble the revolver to reload any longer. Instead the user would put the gunpowder and ball into the chamber that is next to the loading window. Then the user would unhinge the ramrod and use the lever to ram the ball into the chamber. The user would repeat this operation until all the chambers were reloaded. The two crossed revolvers in the picture above are Colt 1839 revolvers.
With the advent of metallic cartridges, the next mechanism that was used was the fixed cylinder/loading gate concept.
In here, there is a hinged loading gate near the back of the cylinder. The gate cover can be slid open and then, metallic cartridges can be removed or loaded one at a time into the loading gate. The cylinder can be rotated after each chamber is loaded, to bring the next chamber in line for reloading. The gate cover is closed after the desired chambers are reloaded. The Colt Peacemaker was one of the weapons that used this reloading mechanism. Since the cylinder is attached to the solid frame of the weapon in both the front and the back, revolvers using this loading mechanism are generally very strong weapons. This is why large caliber revolvers that fire powerful cartridges tend to use this reloading mechanism. The disadvantage of this mechanism is that each chamber needs to be loaded/unloaded one at a time.
The next reloading mechanism we will study is the top-break mechanism. In this mechanism, the revolver is hinged near the front-bottom of the cylinder.The user can open the revolver as shown in the picture above and load new cartridges in quickly and easily. In fact, many users use a speedloader, which is a simple device that holds the cartridges in a circle corresponding to the chambers of the revolver. A picture of a typical revolver speedloader is shown below.
The user simply puts the speedloader on top of the cylinder and unlocks the speedloader, which drops all the cartridges simultaneously into all the chambers of the cylinder.
In the picture above, you can see the old cartridges being expelled by the extractor of a Smith and Wesson revolver as it is being opened. In many models, the auto-extractor is powerful enough to eject the fired cartridges, but is not strong enough to completely eject the longer, unfired cartridges. These are merely lifted away from the chambers by the extractor and not ejected out of the weapon completely.
The advantage of the top-break design is that it allows faster reloading as all the chambers can be loaded simultaneously. If the weapon has an auto-extractor, then the reloading becomes even more faster, as the user doesn't need to manually extract the old cartridges. The disadvantage is that the design isn't as strong as the fixed cylinder design and cannot be used for high-powered cartridges.
The next mechanism is the swing-out cylinder mechanism. In this, the cylinder is mounted on a pivot that swings out and down.
Public domain image from wikipedia.com. Click to enlarge.
As can be seen in the picture above, the rod in front of the cylinder unlocks the mechanism and allows it to swing out. The rod can then be pushed in to operate the extractor and eject out the fired cartridges. As with the top-break design, the extractor is designed so that unfired cartridges are not completely ejected from the chambers. Loading can then be done one at a time, or simultaneously using a speedloader. After loading, the cylinder is pushed back to the body of the revolver and then locked in place.
In the above diagram, you can see the close-up of the star-shaped extractor plate. When the revolver is closed, it sits flush with the cylinder. When the extractor plate is pushed away from the cylinder, it catches the rim of all the cartridges loaded in the cylinder and pushes them out of their chambers.
This is a modern design and is much more sturdy than the top-break mechanism. However, it is not as strong as the fixed-cylinder design. On the other hand, it is much faster to reload than a fixed-cylinder model.