Good Morning bsteele;

I had not thought of the old process of drilling a cavity and then filling it with lead as a method of recoil reduction, but I know that proceedure was widely practiced is times past.

I, or course, could carve out the wooden plug and verify your theory of a lead slug implant. However, the cavity just may have been filled with liquid mercury instead of solid lead.

Regards,
Dr.W.E.Brown