As Rhy said, supersonic speeds are higher than the speed of sound, that is about 950 km/h (depending on weather etc.). small bullets may travel with this speed, rifle ammo goes up to 3*sonic speeds. I have no idea how they funtion in space - and you also need to consider the speed of the ship, that is a lot faster than a walking man, or a bus. Spaceships may accelerate continously to something like 30'000 km/h, so they are much faster than a bullet - you even couldn't hit them with a firearm. I think in space you'd need to use rockets that are accelerating themselfs too.
Imagine the worlds surface moves/rotates at about 1600 km/h, so when you shoot a supersonic rifle bullet in the opposite direction, the bullet may just float in mid air.
Imagine the worlds surface moves/rotates at about 1600 km/h, so when you shoot a supersonic rifle bullet in the opposite direction, the bullet may just float in mid air.