Ballistic and Test Evaluation System; The propellant grain geometry used in most high power reloadable motors; the grain has a central core, the length of each grain is ~1.5 time its diameter and the ends are uninhibited; the grains burn from the ends as well as the core, making each grain shorter as the burn progresses; the shortening of the grain makes the burn more regressive, almost exactly balancing the progressive nature of the core expansion