it depends on the twist rate of the rifling. Lee makes moulds that are 450gr and 500gr as I recall. Even the lighter bullets in the .50 are going to do the job. I use very short bullets in my .577 Sniders. 320gr round ball and 430gr conical, anything longer and I cannot hit my targets as the twist is so slow. I am not sure of the twist on these Sharps .50's, but try to match the bullet to the twist.

Perhaps someone knows the ideal bullet for these rifles?