APFSDS stands for Armor-Piercing Fin-Stabilized Discarding Sabot. It is a type of ammunition used in modern Main Battle Tank guns. This type of round, once it has exited the muzzle of the gun, discards a set of buffers from around the central core of the round. These are extremely light and serve only to gather the kinetic energy of the round's propellant; when they drop off, the kinetic energy of the remainder of the projectile is not significantly diminished. The core of the round is made of a cylinder or rod of extremely dense (and, if possible, hard) material such as osmium, depleted uranium, tungsten, or if cost is a significant factor, steel; although Iraqi tank crews discovered the hard way that steel-cored shot wouldn't penetrate modern tank armor in 1991). This dense, hard core goes on to (hopefully) hit the target, at which point all of the kinetic energy in the shot (minus the buffers and friction, naturally) is transferred to a small point on the target. Usually, this is on armor plate. This small cross-section, coupled with the high energy due to the density of the penetrator, allows for rather impressive destruction of targets protected by even extremely thick and/or high tech armor.

See also: HEAT, HESH

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