... the kind with five firing pins, for Colt-style percussion revolvers: can they be
carried with five rounds? Is there a provision to rest the hammer between
Yes there are 5 shot cylinders made so that you can place hammer between specific rounds 1 and 5. There are also conversions with a single firing pin that can be made so it has a reloading gate. Problem with these guns is the issue of selling them later is questionable, as it has then been converted into a cartridge gun. So to stay out of trouble do not buy used but assemble your own. Cylinders are avail for 1861,60,51, dragoon models, baby dragoon models, Remington Army, Navy, 31 revolvers. They are maker specificPietta or Uberti so acquire the gun first. There is also a .22 conversion for the Remington available now, as I understand.
Almost forgot. Gunsmith at Ahlman's in MN told me to NEVER release the hammer from half cock without pulling to full cock and releasing it. So I would think the dropping hammer between rounds may be hard on gun. If I was going to get one of these 5 round cylinders I'd get a gunsmith DVD and learn to redo the timing myself. Keep it tight will cut down on wear. As the timing gets off wear increases exponentially