I just found this forum today and I know this question was asked last Oct. but it is easy to load BP in a 45-70. First off I would use Goex Cartridge Grade or FFG BP or Pyrodex Select. It does not matter what the weight of the charge is exactly. You need to use a drop tube at least 24 inches long to trickle the powder through. You use 3/8 inch copper tubing for the drop tube. You will need to get some Walters Wads 30 thousands thick, Cabela's has them or do a search to find other places. Trickle enough powder down the drop tube to fill the case up to the point that you can place a wad on the powder and compress the wad down about 20 thousands of an inch and have enough room to seat the bullet to the correct length. Use a hot primer like Fed. 215 and you need to use a bullet lube make for BP cartridge like SPG lube. The lube keeps the fouling soft so the next round will push it out of the way and shoot accurately. When you get done shooting you will need to clean your cases with hot soap and water and use a nylon 45 cal brush on the inside of the cases and let them air dry. Clean your rifle with any BP solvent or soap and water. I have also used Fantastic with orange oil to clean the bore and it works great. Do a search for BP Cartridge shooting to learn more. Long Range BPCR .com Home Page
is one place. I shoot a Sharps copy in 45-70 and it will shoot 2 1/2 inch 10 shot groups at 200 yards regularly. This is with a vernier tang mounted open sight 28 inch barrel and a 500 gr. RCBS BPS cast bullet lubed with my own lube made from 50% bees wax 40% olive oil 10% STP oil treatment by volume, 62 grs Goex Cartridge BP, WW case, Fed. 215 primer, 1100 fps.
I have killed deer with this rifle and never recovered a bullet. It will shoot through a deer from chest through the butt and keep going so be careful of what is behind and beyond what you are shooting. A bull dozer does not have to be moving fast to do a lot of damage. Oh! Paul A. Matthews has some very good books on loading and shooting the Black Powder cartridge rifles. SPG lubricants also has a very good book for loading BP Cartridge.