Sabot A sabot is a device used in a firearm or cannon to fire a projectile , such as a bullet , that is smaller than the bore diameter , or which must be held in a precise position . Design . Since a strong seal is needed to trap propellant gases behind the projectile , and keep the projectile centered in the barrel , something is needed to fill the undesirable but necessary gap between projectile and barrel , a space referred to as the windage , and this 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 or papier - mâché - in cannons ) , 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 carries 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 . Sabots are used to fire the flechettes that form anti - armour kinetic energy penetrator s . A sabot is also used to fire anti - personnel flechette rounds . This round consists of the outer cup ( sabot ) which holds numerous subcaliber darts . The sabot cup holds the individual flechettes together tightly until the sabot case separates after leaving the barrel . For reasons why a smaller diameter projectile can be desirable , see external ballistics and terminal ballistics . 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 . Types of sabots . Cup sabot . A cup sabot merely supports the base and rear end of a projectile . When the sabot and projectile exit the muzzle of the gun , air pressure on the sabot forces the sabot to release the projectile . Expanding cup sabot . Used typically in small arms ( most commonly muzzleloader s ) , an expanding cup sabot has a one piece sabot surrounding the base and sides of a projectile . Upon firing , when the sabot and projectile leave the muzzle of the gun , inertia from the rotation of the projectile and sabot opens up the segments surrounding the projectile , releasing it . Base sabot . A base sabot has a one piece base which supports the bottom of the projectile , and separate pieces that surround the sides of the projectile and center it . 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 sabot . A spindle sabot uses a set ( usually two ) of matched rings which have a center section in contact with a long projectile , front sections which center that projectile in the barrel , and a rear section which both centers the projectile and seals propellant gases . Spindle sabots are the standard western type of armor - piercing ammunition . Two - and three - piece spindle - type sabots are shown in the illustrations at the right of this paragraph . Shotgun slug s often use a cast plastic sabot similar to the spindle sabot . Shotgun sabots in general extend the full length of the projectile and are designed to be used in rifled barrels . Ring sabot . 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 .