Going to a conical is heading in the wrong direction IMHO. Unless a fast enough twist,ie like for a Sharps etc I'd stick with the round ball. I finally got my Sharps 40-70 to work OK on deer, but only after switching to a castbullet with a .300+meplat. ie a flat nose. In the usual muzzleloader, I prefer round balls, 'cause they work. Pressures are going to go way up with a conical of any decent length. Velocity will drop, over what you can get with a RB, so I don't see much of an advantage when talking deer hunting. I have a .50, a .54,a .62, and up etc so I don't use my .40 for deer; but if I did, I'm certain that awell placed shot
with my load of .395 ball and 60 gr 3 F would drop one.