From Wikipedia: The AT4 (also variously AT-4, AT4 CS, AT4-CS, or AT-4CS) is an 84-mm unguided, portable, single-shot recoilless smoothbore weapon built in Sweden by Saab Bofors Dynamics (previously Bofors Anti-Armour Systems). Saab has had considerable sales success with the AT4, making it one of the most common light anti-tank weapons in the world.
All I really know is that this puppy makes a giant “Boom” followed closely by another farther away “Boom”. It’s impressive.. that’s to say, I walked about 800 meters, still being another 200 meters from the range, and this thing woke me up from a dead sleep. It’s darn loud.