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