AP-Guns are weapons, which shoot a beam of Anti-Protons (APs) at near speed of light (99 PSL). Anti-protons that hit mass (the enemy ship) destroy it. An AP Gun is not effective beyond about 4 light seconds. They are the default weapon installed in turrets of Commonwealth ships and in Slipfighters.
When the APs hit Protons (like in every atom), they annihilate each other and damage the atom or in a larger scale, the target object. This weapons are only effective in a distance less than 4 lightseconds.