I have an older ASM-made 1861 Navy in 44 Colt, a First model Richards Conversion replica. I bought it used but in like-new condition, for 400 bucks at a gun show. It shoots very well and seems to be better metallurgy than most of the cap/ball Italian replicas. The arbor is a much firmer fit, and the wedge/barrel/arbor interface much better steel quality and hardness than a cap/ball, and it doesn't shoot loose like a cheap cap/ball pistol does.
If you want a bomb-proof Colt pattern cap/ball pistol, retrofitting a cartridge conversion would be a roundabout, expensive and difficult way to get one- and not well advised- better options would be get a Centaure Belgian Colt (those have frames machined from forged steel blanks), or one of the Italian replicas in STAINLESS STEEL. Or just give up on the open top Colt design, and go to a Remington replica, or a Ruger Old Army. Uberti also made a Colt 1873 Peacemaker pattern in cap/ball that is interesting and would be strong.
It has been my experience that any of the Italian made Colt open top guns will shoot loose in varying amounts of time, some last longer than others, although Uberti may have finally got it right with true forged steel frames (the info is vague on that). The old brass frame replica Colts are the biggest joke in the shooting world, for actual shooting. A steel arbor threaded into a brass frame, that is being stressed by gunpowder explosions, it not conducive to reliability. There's not a lot of material in the frame around that arbor to thread in to, being the hand slot is right next to it. Eventually the end shoots off the gun and the barrel/cylinder goes downrange with the round ball. It "drops the arbor" in shooting lingo. Regardless, even the brass frame replica Colts are becoming collectible to some degree as of late, because most of those Italian replica companies are now out of business, and collectors are starting to buy up different barrel addresses made by various dead Italian replica companies, such as ASM, COM, DGG, Replica Arms, etc. There's only 2 left making the pistols, that is Uberti and Pietta. The rest have been bought out and consolidated.