The original minnie ball for the (mostly contract) rifled .69 muskets prior to the Civil war, was hollow based of course, .69 cal. and 730gr. If these fit 10 bore wad cups, they should be an accurate bullet of decent size for a rifled 10 bore. Lyman makes the mould, still. I have one, but have not tried any in my .69 rifle as of yet.

The .69's were the most accurate minnie rifles in the arsenal, outshooting for range and accuracy, both the .54's and .58's.