Extrudable priming mixture comprising 32-42% normal lead styphnate, 14-16% antimony sulfide, 30-33% barium nitrate, 3.9-4.1% tetracene, 6-8% aluminum powder, and 41/2-8% binder comprising the liquid monomers methyl methacrylate and trimethylolpropanetrimethacrylate, is solidified to a material of admirable percussion sensitivity by radiation polymerization of liquid monomers therein.