My Lyman mold does have the beveled base. They patterned their molds after the Winchester molds of the day, which all cast a beveled base bullet. There are only two reasons a bullet will keyhole. Either the barrel has a bad bore, or the bullet diameter is too small for the bore size. You've got to match the bullet to bore diameter when shooting black powder. It may have an oversize bore and the mold won't cast a bullet large enough. You also mentioned that you are shooting 62 grains of FF Express. If I read your post correctly, you're shooting a .45-60 right? With 62 grains of Express, you're probably pushing the bullet too fast. If you continue to use the Express powder, drop your charge to 55 grains, use a card wade and correct any problems you might have with bullet versus bore diameter. See what happens. Let us know.
Adios,
Buck