Find the 8th edition of Handloader's Digest (1978) for detailed answers to your questions.
On page 46 is an article by John Lachuk entitled, "Caplock Revolvers and Jacketed Bullets."
Here's the gist:
1. A Ruger Old Army, Hawes Remington 1858 reproduction and a reproduction Colt Walker, made by Navy Arms, were used.
2. A .451 inch fluted reamer was used to open the Walker and Remington chambers, so they would accept a .451 or .452 inch jacketed bullet.
3. The chambers of the Ruger Old Army measured .450 inch, so Lachuk polished the chambers to .451 inch.
4. Without reaming the chambers to a larger size, the jacketed bullet could not be seated --- so don't try to seat a jacketed bullet without this modification!
5. Bullets used were the Hornady 185 gr. hollow point, Sierra 180 gr. hollow core, Speer 200 gr. hollow point, Speer 200 gr. swaged lead bullet and Lyman 137 gr. cast lead ball.
5. Both FFFG and FFFFG black powder were used. as was Pyrodex (a recently introduced propellant back then).
6. Lachuk used FFFFG black powder but I don't advise it. This finely grained powder has shown, time and again, a propensity for jumping pressures. Couple that propensity with the harder, friction-creating jacketed bullet and you may blow a chamber.
7. Lachuk also used a small priming charge of Bullseye smokeless powder, in the chamber, next to the nipple. Again, a very dangerous thing to do. Black powder revolvers, no matter what their year of manufacture, are not designed for the pressures of smokeless powder. It's a matter of their design, not metallurgy. Anyone who uses smokeless powder in a cap and ball revolver is a damned fool.
8. Velocities: I know you're all slobbering and chomping at the bit to hear about velocities, so here goes
RUGER OLD ARMY
The 185 gr. jacketed bullet delivered 938 to 1,069 fps, depending on the load.
The 200 gr. Speer hollow poing ranged from 878 to 1004, depending on the load.
The 200 gr. swaged lead semiwadcutter delivered 840 to 960 fps, depending on the load.
The Lyman 137 gr. lead ball delivered 942 to 1,089 fps, depending on load.
HAWES REMINGTON
The 185 gr. Hornady hollow point delivered 904 fps.
The 185 gr. Sierra delivered 994 fps.
The 200 gr. Speer hollow point delivered 909 fps.
The 200 gr. Speer lead semiwadcutter delivered 841 fps.
The Lyman 137 gr. lead ball delivered 990 fps.
Navy Arms Colt Walker
The 185 gr. Hornady hollow point delivered 1,100 fps.
The 185 gr. Sierra delivered 1,167 fps.
The 200 gr. Speer hollow point delivered 1,075 fps.
The 200 gr. Speer lead semiwadcutter delivered 984 fps.
The Lyman 137 gr. lead ball delivered 1,172 fps.
9. The cylinders of each revolver had to be loaded on an arbor press. It was not easy to seat the very hard copper jacketed bullets or, in the case of the Walker and Remington, there was too little space to get the bullet under the revolver's rammer.
This makes the project very specialized and certainly not much good for field use.
10. Lyman cap and ball grease was squeezed over the jacketed bullets after loading.
11. A Ransom Rest was used for the revolver; grip adapters not being made for the Walker or Remington. Accuracy testing was confined to the Ruger; Lachuk didn't say what kind of accuracy he got with the Remington or Walker.
12. At 50 yards, jacekted bullets were consistently more accurate than lead balls. Ruger 10-shot groups ran 4 inches, center to center, for the Hornady, Sierra and Speer bullets.
The best 50 yard group was with Sierra Jacketed Hollow Cavity bullets, at 2-3/4 inches.
At 25 yards, jacketed bullets and round balls both clustered 10 shots around 2 to 3 inches.
While it was an interesting experiment, doing so would require some alterations to the revolver and specialized equipment (arbor pressa and .451 inch fluted reamer with lathe or drill press). I don't think it's the kind of thing the typical cap and ball shooter would find easy or appealing.
And it should be noted that jacketed bullets create far more friction than lead. This friction can dramatically increase pressures.
I wouldn't want to risk any of my revolvers, or my flesh, for a project of dubious value.
Lead balls or conical bullets work fine, whether for plinking or hunting. I can't see much advantage to using jacketed bullets in a cap and ball revolver, when you consider all the prep work that must be done, and the danger of higher pressures that accompany the practice.
