Tactical training round
From Halopedia, the Halo wiki
A Tactical Training Round is a round used to simulate live fire.
Background
It has a plastic polymer shell that helps maintain the actual characteristics of bullet flight. Inside there is a proximity fuse that dissolved its shell when the round comes within 2 centimeters of a surface. Once dissolved, a blob of red paint splatters through the air. The paint also hides a powerful anesthetic and immobilizes the nanofibers woven into clothing causing it to harden. The target then loses the ability to move the hit body part, simulating a bullet wound to the area. The rounds also have a tranquilizing effect caused by the anesthetic.
The rounds are known to be used in MA5B ICWS Assault Rifles, M6 Magnum Sidearms, and BR55 Battle Rifles [1]
