I have a C Sharps Arms 1874 Long Range Express rifle in 50-140 3 1/4. I have been shooting this rifle for about 6 years. Here's what I've found that the gun likes and dislikes.
I first tried shooting a 450 grain cast Montanna Armory bullet in it with 125 grains of FFG. The gun was very inaccurate and I couldn't even get it on paper at 100 yards! I am using Bonanza brass, with a Federal 215 Magnum Rifle primer, and a cardboard top wad. The bullets were ran thru a .50 cal lubersizer. After much fiddling around I finally got it to shoot on the paper but the accuracy was terrible.
I next tried the Montana Armory 600 grain cast bullet with the same powder charge and got it to shoot on the paper about a 6" group at 100 yards.
In discussion with some other folks I learned that the 50s like heavier bullets. So I called Steve Brooks and he made me a mold for a 700 Brooks spire point. What a beautiful bullet this mold throws too! Now the gun shoots 4-4 1/2" groups at 100 yards and I think it's capable of better.
This gun produces horrendous recoil. I am not recoil sensitive having shot a Weatherby 460 and a 338-378. After shooting 20 rounds thru the Sharps it makes my entire right shoulder and deltoids black and blue. Does it bother me that much ? Nope, I love shooting this gun. If you are the least bit flinchey with a lighter gun then don't shoot this thing. If you want to try something really unique then by all means shoot this big fifty.
According to the Winchester book the 50-140 was introduced as a cartridge for the 1886, there seems to be some confusion as to why this cartridge was chambered in the Sharps rifle. Some people even confess that they don't know where this cartridge came from. I'm not sure either, I'm just telling you that I read it in George Maddis's Winchester Book.
Is it overkill for bp silhouette shooting? Yeah probably, would I shoot it in a match? Sure! I also have no doubt that with the proper bullet this cartridge would take down anything on the planet, and even a T-Rex or two. If you saw what the 700 grain bullets do to the steel practice rams at my gun club you'd understand why I say this.
This is a great black powder cartridge much malinged by people who don't have the oomff to shoot it. If you can't handle it then don't shoot it but don't put it down because you can't shoot it.
The Bonanza brass that I've been using isn't the most uniform stuff I've ever used. I found run out in the thickness of the bases and had to turn the bases down on a lathe so they would chamber and extract from the Sharps. It doesn't take much to get the base to specs so if you do this be careful how much you take off. BP has a lot lower pressures than smokeless so we can probably get away with this. I've shot these cases in my gun with no problems and they exhibit no ill effects, cracking, pressure signs etc. All you need is just enough to allow the extractor to grab onto the rim, and for the block to close. If it's too thick you can't lock the block in place and trying to get it back out after it's shot is not fun. Been there and done that.
Like I said this is a great cartridge and fun to shoot, I love it. I hope this gives some folks a little insight into what I discovered with this gun and cartridge.