100 parts polybutadiene polymer, 5-10 parts metal acrylate or methacrylate cross-linking agent, 5 parts zinc oxide as the density modifying material, 2 parts dicumyl peroxide as the free radical source, and X part(s) metal powder filler, such as tungsten or other heavy metals, wherein X depends on the desired specific gravity of the batch and wherein X is a number, integers and real numbers, In a