The newer M16A2's and their on out could stabalize both rounds. Some of the M16A1's still in the inventory cannot stabalize the new round. The green tip is to make certain the new rounds aren't put in the older guns. Since the round was heavier than the old M193 (62grs. vs. 55grs.) their was a change in rifling to accomodate the heavier bullet. Aug 14, 2005 · Cartridge, Caliber .50, Tracer, M1 Used by M2 and M85 machine guns. The tracer is intended to permit visible observation of the bullet's in-flight path or trajectory to the point of impact. Limited to continental US for training purposes only. Trace range: 1,969 yards (1,800 m) Tracer: R256 The cartridge is identified by a red bullet tip.