Re: what is heavier than lead shot
A solid slug of carbide would do.
Just melt it down and pour it in, hehehe!
As mentioned above, the toungsten powder for bullet cores is also denser. melt the lead and pour it in, that will not leave the dead space and deadblow hammer effect.
If you have something that you disassemble and reassemble enough times, sooner or later, you'll have two!