Here’s something informational for Sunday, Nicholas Moran explaining exactly how a modern 120mm (AKA 120×570mm NATO, the type used by the M1A2 Abrams and the German Leopard 2) APFSDS round works.
He has a dummy blue round to demonstrate the features. “All the projectiles are color coded. Explosive, for example, would be green with yellow lettering.” APFSDS rounds are black.
“The aft cap is the one piece which is left behind after a modern round is fired, and this takes up a lot less room than a traditional shell casing rattling around inside the tank once you fire it.”
A long primer rod runs up the middle for more even propellent burning.
“A modern tank does have a firing pin. It’s electrically fired, but it has a firing pin. It looks just like a firing pin you’d expect from a rifle, except it’s about yay long…Electricity goes through the firing pin, sets off the primer, which sets off the propellant, which gives you the big boom.”
There are even emergency hand crank firing systems with dynamos to use if the electrical system goes down.
“The rest of the shell casing is made of a form of cellulose, and it is burned up in the explosion. So the aft cap is sufficient to seal the breach instead of requiring the entire casing to expand as you you’d find on a traditional round.”
“The catch is that this is simply not as robust as a metal shell.” Which is why the loader has to inspect rounds for scratches or bulges to the water-resistant coating. That could cause the round to break apart or misfire. “This is a bad thing.”
Which is why tank crews practice misfire drills to ensure safe handling of rounds so they don’t spread loose propellant all over the tank’s interior.
“The kinetic energy penetrator is itself a dart… it’s got fins at the back to keep the pointy end forwards, and it is kept centered as it goes down the tube by these sabot petals.”
“Modern sabots seem to have settled on three of these petals per projectile. Once the projectile has left the muzzle, the air is caught by the petals and they are peeled away.”
The discarded petals are a danger. “This is why sabot rounds such as APFSDS or M-PT should not be fired over the heads of friendly infantry.”
“The dart goes that way, hits metal, and basically punches through, taking little bits of metal inside with them. This is called a spall. These little fragments metal are extremely unhealthy to anyone or anything inside the vehicle which it hits.”
“However, if the armor is too thin to produce spalling, you get what is known as over-penetration. So you make a dart-sized hole on one side of the vehicle, a dart-sized hole on the far side of the vehicle, and dart sized holes on anything in-between, and outside of brown pants for the crewmen, quite possibly nothing else.”
“If so you’re firing such a target, you’re probably better off using a shaped charge round such as HEAT.”
He then show off a dummy HEAT projector, which has a funky blunt circular head that “in effect clears the air as a wind shield for the decidedly non-aerodynamic flat bit. The main body of the round also performs something of a stabilizing function and thirdly provides adequate standoff or room for the penetrating jet to form.”
“Here is a metal cone surrounded by explosives. The explosives detonate, the cone collapses the liner.”
Text popped up on screen at 9 minutes in notes that the penetrating jet is not high temperature plasma.
Here’s another video that provides a visualized simulation of how APFSDS rounds work.