The mold is for your Henry Dr, is it not? Almost all Henry rifles had a tapered bore and HENRY rifling. You need to cast a slug at the end of the barrel and then turn the slug in the jaws of a micrometer and turn down until it gets harder to turn. This will give you a really close value for the size bullet you need. Henry rifles were made for PAPER PATCH bullets, that is what I would use. I would guess the taper cut the patch as it went down the bore and the lead slug emerged clean.