There is a projection on the side of the hammer that lifts the "hooked leg" of the cylinder bolt. As the hammer is drawn back, it lifts this end of the bolt, which withdraws it from engaging the cylinder notch. (Doesn't this sound heady?) If that stud on the hammer is worn or altered, or it the leg is bent, it won't engage properly. Either a new hammer, or bolt is required.I've got an old Iver Johnson Cattleman here. It looks, by the parts pic very similar to the Colt army revolver.
Short story, I've just started doing some light gunsmithing. Someone I know has the revolver above, and when purchased the trigger was WAY too light.......I'm talking beyond hair trigger. Years later, the gun finally has problems. It was like the hammer would stick down. Once freed, everything seemed to work fine, but it happened every shot. Friend took to a gunsmith who replaced at least the hammer, and maybe the trigger with parts from a Uberty. Gun doesn't work right.
Next gunsmith says "no, wrong parts" and replaces at least the trigger.
Here's where I get it. Half way back on the trigger, it hangs. The bolt isn't dropping out fast enough. At safety cock, the cylinder won't turn to load. The cyl has ever so little play at full cock, and at lockup it's solid, so the had timing is correct, but the bolt doesn't clear the cylinder locks before the hand starts to rotate the cyl, which causes the hang.
I can't get a new bolt, but I can get a new trigger and hammer. I just don't know if the bolt was replaced in one of those fix attempts, or modified along the way.
So, can the bolt be sped up? I don't have a really good drawing of the engagement, so I'm not sure how it's moved to be honest. All I know is that the gunsmiths arround here apparently aren't as detailed as I seem to be, so i trust myself on a first look more than I do them.
The Iver Johnson Cattleman is made by Uberti, modern Cattleman parts, from Numrich or Brownell's, wolud be correct replacemnets. If, as you say, the gun is "beyond hair trigger", I'd suspect the hammer to be the culprit.
P.S. I'm no gunsmith, but I have worked on my single actions.
And, P.P.S. Why can't you get a new bolt?