Interaction of Revolver Action Parts

You may have noticed that something else is missing from our relic revolver. There's nothing that will make the cylinder revolve! To see how all the parts relate, we'll go to our reproduction gun.

Looking into the area where the cylinder fits, the gun is currently at rest. The cylinder bolt is up, locking the cylinder. The hammer is completely forward and the back of the cylinder recess is empty (notice the open slot to the right side).
Pulling the hammer back to the half-cock position, the cylinder bolt drops, unlocking the cylinder. Notice that a metal wedge, the "hand" has come up the slot to the right of the cylinder recess. This pushes on the notches at the rear of the cylinder, starting to rotate it. Because of the geometry of those notches, and because there's as spring pushing the hand forward, the cylinder can be ratcheted by hand to rotate it for loading.
Pulling back to the full cock position, the hand continues to rise. This puts the cylinder into alignment with the barrel. The bolt comes up to lock it into position. Coordinating all these steps is known as the "timing" of the revolver. It is done by careful adjustments of the geometry of the action parts by a gunsmith with a file.
The hand rides in a slot cut into the frame along the near side of the hammer recess. It has a tenon at its base that fits into a hole in the hammer and a spring that rides along the hand recess of the frame. The geometry shown is at full cock.
Looking from the other side, we see the cylinder bolt in relationship with the recess of the hammer. This alignment is the half-cock position. The stud on the hammer has raised the leaf of the bolt, lowering the bolt and unlocking the cylinder. Pulling back the hammer to full cock allows the springy leaf of the bolt to snap forward, raising the bolt and locking the cylinder.