Ballistic and Test Evaluation System; T' propellant grain geometry used in most high power reloadable motors; t' grain has a central core, t' length o' each grain is ~1.5 time its diameter and t' ends are uninhibited; t' grains burn from t' ends as well as t' core, makin' each grain shorter as t' burn progresses; t' shortenin' o' t' grain makes t' burn more regressive, arrr, almost exactly balancin' t' progressive nature o' t' core expansion