The AT4 is an unguided, recoilless and disposable anti armour weapon. It was first developed for the Swedish army (where it is designated m86) by Bofors. Its effective range is 300 metres against moving targets and 400 metres against stationary targets. It is intended for use against all armoured vehicles, though tanks can only be effectively engaged from the side. (Swedish army manuals recommend using at least three AT4s when trying to take out a MBT.) Due to its recoilless design it can be fired from any position, even standing (firing from a standing position generally results in a less accurate shot).
There are a number of versions of the AT4. The most common one is the HEAT version. It carries a 1.8 kilo, 84mm, cone-shaped warhead capable of penetrating 420mm of armour. The main load is 440 grams of Octol and the primary load (what's the difference?) is 17 grams of pressed Hexogen. The velocity of the warhead upon exiting the barrel is 285 metres per second (~1000 km/h).
Other versions are the HEDP version for reinforced structures, the HP (High Penetration) model able to penetrate up to 600mm armour and the CS (Confined Spaces) version with a very small back blast for use by urban warfare units when firing inside buildings (the other versions have a back blast of approx. 15 metres). There is also a version that will be able to take out a MBT in development, designated MBT LAW.
There are two training versions of the weapon; one version for 9mm tracer ammunition and one for 20mm practice projectiles.
Instructions on firing the AT4 can be found on the barrel.