The Ex-B (explosive-bolt) is an alien experiment that involves equipping the guardian drone model of defensive robot, with a cannon that fires spheres of energy that explode upon impact. The Ex-B has a very long range, and if aimed manually, can be used as an effective sniper. It is also notable, that the Ex-B can be shot effectively underwater without adverse effects.
The drone cannon, however, is an ineffective V.A.T.S. weapon, as the fired projectiles will arc toward their targets; since the game does not compensate for gravity in V.A.T.S., this can leave projectiles several meters away from their intended targets.
In the southern area of the weapons lab, there is a room where one can use a nearby button to spawn-in brahmin for the drones to kill (not the room next to the shooting range, but the room next to the weapons cache). Enter the room and kill the drone for the weapon. There is also a second one in the same room that is automatically activated when the first is destroyed.
xbox360ps3pc When shot, the projectile will occasionally pass through walls or the floor and do nothing. [verified]
xbox360ps3pc In some accounts, when shot, the projectile will just disappear as soon as it hits the target, damaging it but not exploding. [verified]
xbox360pc When shot into deep water, the projectile will disappear, and then reappear and seemingly "float" in place on the surface without exploding. Projectiles fired onto the floating projectile will attach and stack, also without exploding. [verified]
xbox360ps3pc In V.A.T.S. mode, the Ex-B seems to aim like a normal drone cannon, landing short of the enemy as if expecting the projectile to bounce. [verified]
ps3 On some occasions, the cannon will fire the projectile but will bounce off surfaces and not explode. [verified]