There are so many different things you can do with a 45-70. The barrel length is important. You really need a faster burning powder for the 45-70 on a pistol. And it is still very tough to outperform a 45 Colt with the 45-70 in the shorter barrel. It can be done, but there is not a lot of difference. I would go with the 405 grain cast bullet, and a fast burning powder. In order to generate a little more pressure I would also go with a heavy crimp on the bullet. That is if you really want the most performance you can get from a short barrel. Are you wanting the most performance, or just a fun shooting middle of the road load??
Crimping in a single shot rifle can be a Ya or Nay. Again it depend on what performance you want. I find that I get better powder burn when I put a heavy crimp on my ammunition. I could not get my 45 Colt to shoot without(in a rifle) a heavy crimp. When I went to the heavier crimp in the 45 Colt the rifle did great.
In my High Walls in 45-70 I do not crimp, and I shoot 40.0 grains of RL7. It burns all the powder in the longer barrel. But this load does not burn completely in a short barreled Encore handgun. However I have never tried crimping this load. I might just try that to see what it does. Tom.
I load RL#7, Fed 210 primers Hornady 300gr hp bullet and another load thats works good is Speer 300gr JHP, AA 5744 powder, Win LR primers I use rem. brass in both loads. I put a lite crimp on these 2 loads.