The Starr double-action army revolver that Clint Eastwood used in "Unforgiven" is currently being reproduced by Fratelli Pietta. As of this posting, Dixie Gunworks has them on sale for $350.00.
The Starr has a rather unique mechanism. Unlike what we generally think of a "double-action" revolver, where you can either thumb-cock the hammer and then pull the trigger, or just take a long pull on the trigger, the Starr essentially has two triggers. The front one, which looks like a conventional revolver trigger, is actually just a cocking lever: all it does is cock the hammer and revolve the cylinder. The firing trigger sits right in the back of the trigger guard, sort of like the exposed sear in the old, cheap Harrington & Richardson and NEF revolvers (and others of the sort). There is a slide with a lug on it on the back of the cocking lever. When the slide is in the "up" position, a straight pull through on the cocking lever cocks the hammer, revolves the cylinder, and then depresses the firing trigger when it's back all the way. When the slide is in the "down" position, the lug on the slide prevents the cocking lever from moving back far enough to contact the firing trigger. You then release the cocking lever and put your trigger finger on the firing trigger for single-action fire. The rear sight is a notch in the hammer-nose, like a Colt C&B revolver, which makes the sights hard to use in double-action mode. I think the reasoning at the time the gun was developed was that the double-action mode would be used in a close-quarters situation where a fast repeat shot was more important than fine aim, while if you had time to aim then the slower single-action mode wasn't going to be an impediment. The Starr, like the Remington, has an enclosed frame, but it is unique in that by removing a knurled thumb-screw the frame can be broken open like a top-break revolver, allowing for exchange of cylinders or easier cleaning (and as far as I know, nobody mass-produces a cartridge conversion cylinder for the Starr). When properly tuned, the Starr wouldn't be a bad choice if you HAD to use a C&B gun, due to the rapid-fire ability and .44 caliber ball. Also, the lack of a cylinder-pin keeps the Starr from jamming due to excessive fouling, and the 12 cylinder-bolt slots allows 6 chambers to be loaded. Unlike the Colt or Remington, which rely on the hammer to lock the cylinder between chambers (and thus could potentially be jarred out of place), once the Starr is locked between chambers by the cylinder bolt you have to deliberately do the long pull on the cocking lever to get the cylinder to turn.
BTW, another reason the round ball is a better stopper than one might guess is exactly due to its ballistic inefficiency: it tends to dump all of its energy in the target, even if it doesn't hit a bone and flatten out.
As for corrosive powder, try Goex Pinnacle. It isn't supposed to be hygroscopic (absorbing moisture from the air) and claims to have an indefinite shelf-life, and is sulfur-free (the burning of sulfur in Pyrodex and black powder, combined with moisture in the air, makes a weak sulfuric acid - the biggest cause of the corrosion). Pinnacle also cleans up with just soap and water. But still a wise idea to fire out all the loads, clean, and reload, just to be safe. Also, if the gun will be stored loaded for an extended period, use beeswax over the balls and NOT Crisco to prevent chain-fire. In hot conditions, Crisco will melt and get into your powder and ruin it. Or, load an Ox Yoke "Wonder Wad" behind the ball.