Probably have trouble finding a load with modern powder for that particular cartridge length. But, I'm sure somebody out there will find one.
Honestly, using a 400 gr bullet in that is kind of underutilizing it. After 1879 the U.S. Army went to a 500 gr bullet in the infantry .45-70. Elmer Keith said it was an S.O.B. out of a Trapdoor carbine.
As ryan said, it'll be a shock to your system to fire.
I use 5744 myself. You do not need to fill the case by any means. 5744 is not position sensitive, no case fillers are required.Depends on your velocity goal
Big and slow, powder that fills the case maybe 5744 ........or Trailboss



























