For use with our Mr Target Indoor Bullet Trap,  the Range Systems Dura-Bloc EXP™ is a patented high-density ballistic rubber composite block designed to encapsulate ammunition up to 7.62 caliber. Self-healing properties seal the bullet’s path after the round has penetrated the surface so each bullet is encapsulated inside the ballistic rubber block. EXP™ Rubber Reduces the Risk of Accidental Tracer Fire. Although the use of tracers is prohibited, independent testing has verified that Range Systems EXP™ ballistic rubber contains properties that reduce the risk of fire from isolated exposure to a low volume of tracers.