R&D Gun Shop
Kirst Cartridge Konverter
Cimarron Firearms Co.
"Metallic Cartridge Conversions: The History of the Guns & Modern Reproductions" Book by Dennis Adler
Links to Black Powder Revolvers (and more history of the cartridge and cartridge conversions)
1851 Navy Cartridge Conversion Manual
Old Western Scrounger
Black Hills Ammunition
For discussion and support:
CAS City (look for the Darksider's Den, NCOWS, SCORRS and STORM sub-forums)
In brief: You can buy a black powder cap and ball revolver already converted to fire cartridges, buy a cartridge conversion cylinder to install in your black powder cap and ball revolver (or have it installed for you), or manufacture a cartridge revolver from a black powder cap and ball revolver.
Thou shalt not:
Fire full-power nitro (smokeless) powder cartridges in a converted revolver,
Convert a brass-framed revolver to fire cartridges, or
Ship a converted revolver to someone who does not hold a Class I FFL.
Lots of things to consider. If, for example, you install a .38 Long Colt or .38 S&W Special cartridge conversion cylinder in a Pietta copy of the 1851 Navy Colt, you will want to have the barrel lined to .357 inch or use hollow-based bullets, because the .38 caliber bullets are actually .357 inch and the bore of a ".36 caliber" Navy Colt is .375 inch. You
can shoot bullets that are .018 smaller than the bore, but velocity and accuracy will suffer.
This problem doesn't exist in the ".44 caliber" black powder cap and ball revolvers because they have a .452 inch bore, which happens to be the right size for .45 Long Colt cartridges. The .44-40 (aka .44 WCF) is .427 inch, and the .44 Colt is .432 inch, so they also need barrel lining or hollow based bullets. The hollow base expands and grips the rifling so the bullet will spin as it goes through the bore.
What you do and get depends on how mechanically savvy you are, how historically accurate you want to be, and of course how much money you want to or can afford to spend.
Go see that bunch of goobers on the CAS City site. Tell them "Frenchie" sent you, ask any questions you have, pay attention to the answers, and don't let them talk you into buying anything that sounds too good to be true or that involves investing in gambling, drinking, or loose women