What a thoroughly inapporpriate deer cartridge!!!!!! Be sure not to tell the hundreds of thousands of dead deer and the thousands of dead buffalo killed by the .44-40 WCF.
Develope an accurate load and chronograph it. I believe that Bill and Mike are shortchanging the old .44 WCF. You will probably get a velocity in the neighborhood of 1200 to 1300 fps. That is plenty of UUMPH to kill a deer at fifty to seventy-five yards.
If your rifle will feed them, I'd suggest a SWC or Flat point bullet design for better game killing effect.
Doc Hudson
P.S. Am I correct to presume that you are familiar with the procedures of Blackpowder cartridge reloading? LMH