I did not know that yesterday!

Ah, an inquiry that warms the hearts of gun-toting physicists. The peacenik response might be...nothing. A gun cartridge holds the bullet or metal tip and the gunpowder (yup, they still use that stuff). The latter requires a spark, a nifty chemical reaction that involves oxygen, which tends to be sorely lacking in space. However, forward-thinking manufacturers have packed an oxidizer within the bullet casing. Whether that's sufficient for an explosive launch is up for much debate.

That doesn't satisfy our bloodlust, does it? We'll assume we can send the bullet on its merry way with the proper gun. The scenario then conjures up the classic physics poser of shooting the monkey. Since we find shooting a cute primate abhorrent, we'll sub in the garden gnome.

Where you're standing when you execute this maneuver, such as within a planet's gravitational pull, would affect the bullet's speed and path. As long as your aim is true, the bullet would travel a straight line (aka Newton's first law of motion) until some sort of force or object impedes it. Meanwhile, the recoil (Newton's third law) has pushed you back with an equal and opposite force.

The next question is, can you fire off another shot? A regular old earth gun likely won't cotton to its new environment and may seize up, blow up, or do something equally annoying. Plus, we've littered space with enough dangerous debris already, do we really need to have bullets go flying?