Sabot (firearms)
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.
More detailed cutaways of the internal structural complexity of advanced APFSDS saboted long rod penetrator projectiles can be found in #External links.
The function of a sabot is to provide a larger bulkhead structure that fills the entire bore area between an intentionally designed sub-caliber flight projectile and the barrel, giving a larger surface area for propellant gasses to act upon than just the base of the smaller flight projectile.
The physics of interior ballistics demonstrates why the use of a sabot is advantageous to achieve higher muzzle velocity with an arrow-type projectile.
Seminal research on two important sabot configurations for long rod penetrators used in APFSDS ammunition, namely the "saddle-back" and "double-ramp" sabot was performed by the US Army Ballistics Research Laboratory during the development and improvement of modern 105mm and 120mm kinetic energy APFSDS penetrators and published in 1978,[1] permitted by the significant advancement in the computerized finite element method in structural mechanics at that time; and now represents the existing fielded technology standard.
Nevertheless, the weight of the sabot represents parasitic mass that must also be accelerated to muzzle velocity, but does not contribute to the terminal ballistics of the flight projectile.
[1] Made of some lightweight material (usually high strength plastic in small caliber rifles, (see SLAP Saboted light armor penetrator), shotguns and muzzle loader ammunition; aluminium, steel, and carbon fiber reinforced plastic for modern anti-tank kinetic energy ammunition; and, in classic times, wood or papier-mâché – in muzzle loading cannons).
Although the use of cup sabots of various complexity are popular with rifle ammunition hand-loaders, in order to achieve significantly higher muzzle velocity with a lower drag, smaller diameter and lighter bullet, successful saboted projectile design has to include the resulting bullet stability characteristics.
However, larger caliber commercial rifles generally don't need such fast twist rates; 1:10 being a readily available standard in 7.62mm.
As a result, the twist rate of the larger barrel will dictate which smaller bullets can be fired with sufficient stability out of a sabot.
