In any case, in Earth orbit it will affect to a greater or lesser degree the atmosphere, and depending on the height of the orbit, the bullet will fly from a few days to a few thousand years until it comes within a distance sufficient to completely burn (in atmosphere). If the shot is far enough from the Earth, the bullet will come into a solar circular orbit.
For any shot, the bullet on any other objectswill never be straight line (straight trajectory) and with a stable speed, and always will be an orbital, even around the galactic center, and the movement accelerated, by the fact that a bullet will be affected by gravity until it with anything not face or burn in the atmosphere of a planet.
as well as the laws of weight. Although the space object was supposed to move indefinitely, but if you try to push "the truck" in space, which weighing about 10 tons, it will not budge.
And I'm also not sure about the bullet speed. my personal opinion, if the bullet hits the iron object in space, it not penetrate heavy iron, because bullet weight is very low.
Of course, I understand that this is a game, and in principle, for the sake of "playing in the open space," I am willing to tolerate absolutely any inaccuracies and violations of the laws of physics. 
