Confusion on how the .50 HEIAP Raufoss round works

[Winston Blake]

Here there is a video (three sizes) about the M82 and its various ammunition. There's one part i don't understand, where the instructor says:

Upon hitting an armored target, that incendiary mix will form adiabatic pressure, that pressure needing to be released will propel the 7.62mm tungsten-carbide penetrator forward at over 4000 feet per second, providing armour-piercing effect on a lightly armoured target.

Globalsecurity gives the muzzle velocity of the Raufoss round as about 3000 fps. So my question is: how does the incendiary in the tip accelerate the penetrator by an extra 1000 fps on impact? What does it mean to 'form adiabatic pressure'?

[AMX]

So my question is: how does the incendiary in the tip accelerate the penetrator by an extra 1000 fps on impact?

Easy: It doesn't. (In fact, an increase in pressure at the tip of the round can only result in it slowing down, rather than speeding up...)
The instructor was, apparently, mistaken.

What does it mean to 'form adiabatic pressure'?

"Adiabatic" refers to a change in pressure, and means that no heat is transferred; it's basically the opposite of "isothermic" (meaning that exactly as much heat is transferred as needed to maintain constant temperature).

"Forming adiabatic pressure" is a not quite correct way of saying "pressure is increased, resulting in an increase in temperature".

Putting 2+2 together, we get 5: The adiabatic pressure increase provides incendiary performance against lightly armored targets (increasing the temperature of the incendiary compound high enough to ignite it), not AP performance.

[Winston Blake]

Thanks, i figured the instructor was a reliable source since the video looked official. Here i was wondering about some wacky boost effect and it was just stupid fuseless detonation.