I have played with over a dozen black powder guns over the years. I have kept only two. One rifle, one revolver.
Both are used for deer hunting during the "primitive weapons" season and have proven effective.
My Ruger Old Army .45 single-action blackpowder revolver, has a 7-1/2" barrel. I have for it two extra fitted cylinders which I ordered from the factory. As the revolver comes from the factory it is sighted for round balls and target loads. To use heavy charges and bullets it needs a higher front sight about 1/8" higher than the one which comes on it. I started by welding a blob of metal onto the existing blade and filing it in to zero, but after a while I decided that the factory rear sight was less rugged than I wanted, so I had a gunsmith set up the revolver exactly as I wanted it. He set back the barrel and recut the forcing cone, line bored the several cylinders I had for quick reloads, shimmed the hammer for a faster hammer throw, did a trigger job, etc. "the works." To me the extra cost was worth it, because the revolver is powerful, accurate, reliable and dependable in the field.
I replaced the original factory sights with Hamilton Bowen's "Rough Country" rear sight, which are sturdy, machined steel, with locking screws, designed for ruggedness in field use. I also had fitted a custom front base having several Holland & Holland type interchangible "caterpillar" blades to enable precise zeroing and clear sight picture. My hunting load with Lee 250-grain R.E.A.L. bullets hit exactly on at 25 yards with all the Pyrodex P or 3Fg black powder that the chambers will hold. A charge of 35 grs. of 3Fg or "P" gives ballistics about the same as a .45 Colt cartridge gun, about 900 fps with the 250-grain bullet. Typical groups fired off sandbag rests are 2 inches or less at 25 yards. It shoots clear through deer from any angle and leaves a good blood trail because the loading lever rammer reforms the Lee bullet into a .45 cal. wadcutter!
I set up this Ruger as a specialized hunting pistol because it was not legal to carry a cartridge handgun during the blackpowder season, but we are bothered with packs of feral dogs and I wanted a quick follow-up shot capability. Carrying a .45 or larger blackpowder revolver along with a muzzleloading rifle is legal for hunting in my state. I have killed several deer with it at short range from my tree stand, and it is quite effective at reasonable ranges within 25-40 yards, where my ability to make well-aimed, vital hits is adequate.
I also have a cartridge conversion cylinder for the Ruger revolver made by Walt Kirst, so that I can shoot .45 ACP ammo in it. This works very well. Any factory load is safe in it and shoots to the sights with normal velocity and accuracy with 230-grain jacketed hollow points, which are effective personal defence or hunting ammunition.
I also have a single-shot, blackpowder rifle, a T/C Renegade rebarrelled with a Green Mountain .50 cal., one turn in 28" twist barrel, being short and handy only 24" long, for bush work. It stabilizes either 370-grain Maxi bullets or sabot rounds well. Firing a T/C Maxi Ball and 100 grains of 2Fg or Pyrodex RS velocity is 1600 fps and I get 2 inch groups at 50 yards or 4-5" at 100 with iron sights. It has also killed about a dozen deer over the years, as we get four tags with the annual licence. I cast bullets for my black powder guns using 1:40 tin lead using a Saeco double-cavity mold modified by
http://www.hollowpointmold.com with Erik's inset bar cup-point conversion. The nose cavities look like the old Webley Manstopper bullets, as if you made a dimple by pushing a .22 short bullet into the nose.
I bought these guns originally for recreation. But after Obama was elected I bought an ample supply percussion caps and Pyrodex to feed them, got the bullet molds and wad punches. I started shooting the Old Army in cowboy matches to get used to the "Pale Rider" method of cowboy combat reloading. I now appreciate why the old West gunfighters carried two revolvers!
I tried briefly several Italian Uberti and Filli Pietta reproductions of .44 Colts and Remingtons. I shot them a great deal over the course of a year. None were as accurate or reliable as my Ruger. In particular, a brass frame Remington loosened up to .020" of end play, sufficient to cause misfires after firing less than 300 full charges of 30 grains of 3Fg and round balls. Cabelas replaced it with a steel one which I shot for a year and even got a Kirst cartridge conversion for it, but it was less accurate, didn't shoot to the sights and overall was a long far cry in performance from the Ruger.
So, my advice is that if you will get only one cap & ball revolver pay whatever it costs to finds a Ruger Old Army with adjustable sights. If limited to the factory sights, use round balls, loaded with as much powder as you can cram into the chambers. That will be about 40 grains of 3Fg which obtains about 1000 fps with a 146-grain .457: ball, kinetic energy of this load is the same as fiuring 38 Special +P or 9mm 147-gr. OSM subsonic.
If really serious about deer stalking with your revolver, spend the money for gunsmith fitting of a 1/8" higher front sight and use the Lee 250-gr. R.E.A.L. and 30 grs. of 3Fg for 900 fps. Once you get a good zero, flood the factory Ruger rear sight with Crazy Glue or Loctite thread sealant so that it will resist recoil vibration and then stay zeroed!
You could make a good case for a companion .45 percussion rifle which could use the same projectiles as the revolver. I did try a T/C Cherokee .45 rifle for a year. I worked up to 80 grains of 3Fg with the 250-gr. Lee R.E.A.L. for 1350 fps and 2 inch groups at 50 yards with iron sights, but recoil of the very light rifle was unpleasant. Its kinetic energy was no more than a .44-40 Winchester, less effective on deer than my .50 cal., which was an absolute stone killer equal to the old .50-70 service round they used to kill buffalo and shoot Indians.
A reliable blackpowder rifle suitable for deer should be not less than a .50 cal. In elk, bear or moose country a .54 cal. makes sense, and is dangerous game capable even with a round ball, firing a heavy load of 100 to 120 grains of powder. Just ask Merriweather Lewis!
I have used roundballs for deer, killing with them well with n80 grains or more of powder in the .50 cal. But, if you hunt with roundballs you must remember that their poor aerodynanics cause them to lose HALF of their kinetic energy in traveling the first 50 yards. So to have an effective 100 yard deer load you must drive them over 1800 fps! Dedicated .50 cal roundball rifles are usually twisted one turn in 66." When I was in New Hampshire I killed deer with a flintlock driving a .495 ball at 2000 fps with 120-grains of powder from a 40" barrel. Pure lead balls flatten on impact and kill much better than a .30-30!
Maxi-Balls and R.E.A.L. bullets need a twist of 48" or faster in the .50 cal. to stabilize adequate. Sabot rounds need 32" twist or faster. A fast twist limits how hard you can drive patched round balls with accuracy. The limit is about 90 grs. of powder in a .50 for 1800 fps in a 30" barrel for about 1800 fps, and 2-1/2 to 3" groups at 50 yards. An adequate 50-yard deer load.
My 28" twist Green Mountain LRH barrel is intended for shooting Maxi bullets or Sabots and does not handle round balls at high velocity, but shoots them adequately with light charges down to about 30 grains of powder for about 1050 f.p.s. from the 24" barrel with ragged hole 25-yard groups or 2" groups at 50 yards, which are just fine casual target work and small game shooting or head shots at deer out my kitchen window into my back yard country garden. Great to save powder and lead in hard times. The energy of such a load is about the same as a modern .40 S&W pistol.
If we were reduced to owning only blackpowder guns, a similar, modest battery would be very much better than having no guns at all. You could feed yourself and they would serve as a defensive deterrent against people who are not inclined to fight when the victim is armed at all. But God help you if you get into a fight with somebody who is armed with modern weapons and is determined to kill you. Then you must accept your fate, make your shots count, make it as costly as possible for the evil ones and take a bunch of the bastards with you....