sabot

A sabot (UK: , US: ) is a supportive device used in firearm/artillery ammunitions to fit/patch around a projectile, such as a bullet/slug or a flechette-like projectile (such as a kinetic energy penetrator), and keep it aligned in the center of the barrel when fired. It allows a narrower projectile with high sectional density to be fired through a barrel of much larger bore diameter with maximal accelerative transfer of kinetic energy. After leaving the muzzle, the sabot typically separates from the projectile in flight, diverting only a very small portion of the overall kinetic energy.
The sabot component in projectile design is not the relatively thin, tough and deformable seal known as a driving band or obturation ring needed to trap propellant gases behind a projectile, and also keep the projectile centered in the barrel, when the outer shell of the projectile is only slightly smaller in diameter than the caliber of the barrel. Driving bands and obturators are used to seal these full-bore projectiles in the barrel because of manufacturing tolerances; there always exists some gap between the projectile outer diameter and the barrel inner diameter, usually a few thousandths of an inch; enough of a gap for high pressure gasses to slip by during firing. Driving bands and obturator rings are made from material that will deform and seal the barrel as the projectile is forced from the chamber into the barrel. Small caliber jacketed bullets do not normally employ driving bands or obturators because the jacket material, for example copper or gilding metal, is deformable enough to serve that function, and the bullet is made slightly larger than the barrel for that purpose, (see full metal jacket bullet and driving band).
Sabots certainly use driving bands and obturators, because the same manufacturing tolerance issues exist when sealing the saboted projectile in the barrel, but the sabot itself is a more substantial structural component of the in-bore projectile configuration (Drysdale 1978). Refer to the two APFSDS (armor-piercing fin-stabilized discarding sabot) pictures on the right to see the substantial material nature of a sabot to fill the bore diameter around the sub-caliber arrow-type flight projectile, compared to the very small gap sealed by a driving band or obturator to mitigate what is known classically as windage. More detailed cutaways of the internal structural complexity of advanced APFSDS saboted long rod penetrator projectiles can be found at reference 2.

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