At less than 50 yards, you should have NO problem killing a deer with that .45. Work up loads from 50 grains going up to 65 grains. Ican tell you from my own observations that 65 grains of FFFg powder beind a .440 ball with a .015" patch lubed in NL1000, ( wonderlube, bore butter, etc) will give you more than 1900 fps. The small ball will drive through the chest of the typical whitetail at short yardage, and enters with a larger hole than most modern centerfire rifles produce when exiting! Shooting my brothers New .45 rifle, with its 37 inch barrel, and 65 grains of powder, we were able to easily hit bang plates at 100 and 135 yards. We would not shoot at a deer at that yardage, but this gives you an idea as to how flat the load will shoot.
A round ball kills by leaving a large( .45 caliber) primary wound channel, and the soft, lead ball expanding quickly on impacting flesh, to make an even larger caliber primary wound channel. Even when the ball hits bone, the bones are thin and easily punctured, the ball driving itself and bits of bone with it through the vital organs. Expect the ball to look like a bloody nickel when it stops. It will be more flat than round, and more like a lead disc, than a lead ball.
Find a powder charge that give you good accuracy at 50 yards, and stick with it for your hunting. Accurate placement is much more important than velocity. To give yourself peace of mind, do some penetration, comparative, testing with your favorite modern cartridge deer rife, and with the .45. I think you will be pleasantly surprised.
