There was a time, about 10 or 15 years ago, when some manufacturers of Sharps clones did not suggest using smokeless powder in the .45-120. Negated your warranty if you used anything other than black powder.
When you say you want, "the biggest and baddest," stop thinking with your cojones. The .45-120 with black powder loads will thump you sumpin fierce!
Get the .45-70 or .45-110. If you want to plink at long range, get the .45-70 for its easy availability of brass and factory ammo. The .45-110 will require reloading, pretty much.
The .45-110 case may be reloaded with .45-70 dies. It may not fully resize the case but as long as you're using the same cases in the same rifle it won't matter much. Eventually, you may have to purchase .45-110 dies to fully resize cases on occasion. Or perhaps not. It all depends on the size of your chamber and how much case expansion you get.
BEWARE of .45-70 loads posted on the internet, or told you by guys at the range.
The 1874 Sharps action is not particularly strong. Modern steels do almost nothing to strengthen it; it's a question of design, not metallurgy, that limits its strength.
Do not exceed loads intended for the 1873 Springfield Trapdoor. The Sporting Arms and Ammunition Manufacturing Institute (SAAMI) limits Trapdoor loads to 18,000 Copper Units of Pressure (CUP). Any loads in the Sharps should be no greater than this, and preferably a little lower. A steady diet of maximum loads (created by using smokeless powder) will strain any gun and accelerate wear.
The Sharps design is not intended for loads in the realm of the Winchester 1886 or Marlin 1895; SAAMI recommends no more than 28,000 CUP in these two rifles. And if you drop in a load intended for the Ruger No. 1 or 3, you'll experience what we reloaders call, "an instant disassembly." The Rugers can take maximum loads up to 40,000 CUP, more than TWICE what the Trapdoor and Sharps can take!
I load black powder and smokeless powders for a reproduction 1873 Springfield (Harrington & Richardson) and a Marlin 1895 (bought both new in 1977).
Black powder loads are fun but require commitment. After each shooting session, the rifle must be cleaned thoroughly with a water-based cleaner. I use plain ol' water with a few slivers of Ivory bar soap. Then the rifle must be dried thoroughly after cleaning, since you're using water.
AND ... you must also knock the dead primers out of your fired cases and wash them immediately in hot, soapy water to remove all black powder fouling.
Black powder are Pyrodex are both corrosive. Black powder contains potassium nitrate, which is very similar to ordinary table salt. It will begin rusting steel and corroding brass in hours, even quicker.
Black powder shooting is fun but don't think you can return from the range, put your rifle away and forget it and the empty cases for a week or two. Many, many black powder guns have been ruined by neglect or ignorance.
ALSO .. don't think that you can reload just any ol' bullet on top of black powder. You'll need to use a very soft lead bullet, with the proper black powder lubricant. Hard-cast bullets with lubricant intended for smokeless powder will cause bad leading. Consequently, accuracy will go out the window in short order.
My advice? Buy a .45-70. Brass, dies, bullets and loads are much easier to deal with. You may safely use jacketed bullets in a modern reproduction Sharps, as the steel is more wear-resistant than the originals.
I shoot lead bullets, cast by myself, almost exclusively in my Marlin 1895 and Trapdoor repro. Wheelweights work fine for black powder loads, but certainly no harder alloy should be used. Pure, dead-soft lead is preferable for black powder. For smokeless powder loads, wheelweights with a bit of 50/50 bar solder added will raise the hardness.
If I were you, I'd get a Sharps in .45-70 and call it good. It will do all you require and not require special care.
