A sabot (: "saybow", or /ˈsæboʊ/: "sabbow") is a device used in a firearm or cannon to fire a projectile, such as a bullet, that is smaller than the bore diameter. The term is also applied to a battery stub case, a device used similarly to make a small electrical battery usable instead of a larger one.
Since a strong seal is needed to trap propellant gasses behind the projectile, and keep the projectile centered in the barrel, something is needed to fill the gap between projectile and barrel, which is the role of the sabot. Firing a small size projectile wrapped in a sabot raises the muzzle velocity of the projectile. Made of some lightweight material (usually plastic in smallbore guns, and aluminium - and, in earlier times, wood - in cannon), the sabot usually consists of several pieces held in place by the cartridge or a loose connection. When the projectile is fired, the sabot blocks the gas, and accelerates the projectile down the barrel. When the sabot reaches the end of the barrel, the shock of hitting still air pulls the parts of the sabot away from the projectile, allowing the projectile to continue in flight.
Sabot-type shotgun slugs were marketed in the U.S. starting in about 1985. When used with a rifled slug barrel, they offer vastly improved accuracy compared to traditional shotgun slugs. They are now legal for hunting in most states.
The base sabot has better and cleaner sabot/projectile separation than cup or expanding cup sabots, but is more expensive since more pieces are involved.
Spindle sabots are the standard western type armor piercing ammunition type. Two and three piece spindle type sabots are shown in the illustrations at the top of this article.
A ring sabot uses the rear fins on a long projectile to help center the projectile, and the multi-piece sabot forms only a single thin ring around the projectile near the front, sealing gases from escaping past it and centering the front of the projectile.
Because the rear fins have to have the same diameter as the gun bore, they typically are larger than is optimum for flight performance.
Several Soviet and current Russian design armor piercing sabot projectiles use ring sabots.