the desired compression characteristics as is well known in the art the type and amount of crosslinking agents used to make the core will have the greatest influence on the core compression achieved in one embodiment a compression of about between 77 and 87 pga nominal is achieved by preparing a compound consisting of by parts per hundred parts rubber polymer phr by weight 90 100 phr high cis polybutadiene 0 10 phr natural or polyisoprene rubber 25 30 phr zinc diacrylate 3 6 phr zinc oxide 15 24 phr of fillers and process aids 0 1 phr of antioxidant and 0 5 phr of a free radical initiator or peroxide as used herein high cis means a cis isomer content of greater than 93 it is to be understood that the core formula set forth herein is but one formula that can be used to make a core having the desired core compression the listed components are dry mixed in a mixer such as a banbury mixer the mixed ingredients are then u201c sheeted u201d on a drop mill and extruded to desired weight and dimensions the extruded plugs are then placed in mold cavities where heat and pressure are applied in one embodiment the plugs are heated from about between 135 u00b0 c and 175 u00b0 c under sufficient pressure to maintain the plug within the mold cavity the plugs are maintained in the cavities under the requisite heat and pressure until cured curing takes place under the designated temperatures when the plugs are maintained under pressure in the cavities for about between 5 minutes to 25.