I'm with Bill - less 'hollowing' needed in the buttstock. Pedersoli used a 1 pound bar of lead in their double barreled Kodiaks. My .58 had a weight of 10 1/2 poinds, way too much for a little .58 Round Ball rifle.

A pound might be OK, maybe 1 1/2 pounds - wire, I think, is a good idea due to the hole already there and the wire might be easier to remove if necessary.