I had the same problems with two different Uberti's. One a Open Top had the bolt popping up to early, peening the cylinder in front of the lead. It was caused by the bolt having to short of a leg, coming off the cam to early. I installed the bolt from a cousin to the OpenTop, a Uberti Richards II. Everything worked as it should have. Called Cimarron and they sent me a new bolt which after slicking it up and checking the timing, all was well. The 2nd one, a Richards/Mason, had the bolt peening the front side of the lead (towards the barrel. Had to do some filing and stone the bolt to shape. Also I adjusted the bolt spring to lessen the tension on it so it wouldn't have as much force on pushing the bolt up through the frame bolt window for the bolt to contact the cylinder. The arbor fit will need to be checked and attended to as well.
Both problems are posted in the 'Gunsmithing' section of this forum. The R/M is on page one, not sure what page the Open Top is on, although I never fully addressed the final outcome as I should have. Thought about doing that several times, should do it in case someone else needs the same Rx to their revolver. Maybe some of the 'House' smiths will chime in on your post and give ya a few pointers. It's frustrating when you pay the $$$ Uberti gets for them and have the problems associated with them. My Richards II has been a problem free child. I have a number of Uberti percussion revolvers and have never had the timing problems I've had with those two cartridge guns.