I had an Italian copy of a three band Enfield back in the '80's and cast some Minie bullets with Lee's 500 grain mould. The rifle must have been bored a little on the large size because I had a fairly large percentage of keyholes on target. I found I could slightly squeeze the bullet end-to-end in a vise and check for a tighter fit in the muzzle by trial and error. That took care of it.

Those slugs that tumbled made a distinct sh-sh-sh sound. In some accounts of battles during the CW, mention is made of that sound and I now know what caused it. If there could be anything worse than having one of those hit you point on, it would have to be sideways.