Re: Reloading for 45/70
Your 1874 Sharps is a relatively weak action. Do NOT use loads intended for the Marlin 1895 or Ruger No. 1 in it.
Maximum loads should be considered as no more than 18,000 Copper Units of Pressure (CUP). It would be best to stay well under that.
I have a Marlin 1895, and a reproduction 1873 Springfield "trapdoor," both purchased in 1977.
A good load for my Springfield has been the Lyman 457193 flatpoint cast bullet, which is about 420 grains when cast of wheelweights or equivalent. I load this over 37.0 grains of IMR3031. I size the bullet to .459 inch and lubricate with the typical beeswax/Alox lubricant mix.
If someday you decide to get a Marlin or other rifle that can take higher pressures, assemble those loads with nickel-plated cases. Use brass cases for the Sharps. This will prevent you from dropping a high-pressure load in that Sharps.
Years ago, I'd take a red Magic Marker and run it up and down the brass case, of the loads I assembled for the Marlin. Back then, no one made nickeled .45-70 cases.
One final warning: Never use a load posted on the internet without first checking it against the website or reloading book of the projectile or powder you're using. This includes the load above, that I just gave you.
There are all kinds of wild claims and excessive loads posted for the .45-70 by folks who have absolutely NO access to a ballistics lab to measure pressures. The manufacturers of bullets and powder DO have labs that can measure pressure.
Some folks like to push the limits with the .45-70. I like my fingers, eyes and guns too much to do so.
"Therein do I see an ugly cat. Smoke. Fire. Brimstone. A vast desert. Holes in parchment. The ugly cat is much amused." --- The quantrains of Gatodamus (1503-1566)