Sabot

[Sarah]

A thick, circular disk of wood, to which the cartridge bag andprojectile are attached, in fixed ammunition for cannon; also, apiece of soft metal attached to a projectile to take the groove ofthe rifling.

[Sarah]

A lightweight carrier in which a projectile of a smaller caliber is centered so as to permit firing the projectile within a larger-caliber weapon. The carrier fills the bore of the weapon from which the projectile is fired; it is normally discarded a short distance from the muzzle. In short - a badass tank round that you don't want to be hit with.