Fires can't burn in the oxygen-free vacuum of space, but guns can shoot. ... Modern ammunition contains its own oxidizer, a chemical that will trigger the explosion of gunpowder, and thus the firing of a bullet, wherever you are in the universe.

Would a bullet be effective in space?

Yes. Bullets carry their own oxidising agent in the explosive of the cartridge (which is sealed, anyway) so there's no need for atmospheric oxygen to ignite the propellant. ... Once shot, the bullet will keep going forever, as the universe is expanding at a faster rate than the bullet will travel.

How fast can a bullet go in space?

Those galaxies are travelling at around 200km/s (124 miles/sec) as the Universe expands, whereas a travelling bullet can reach speeds of only 1km/s (0.62 mile/sec).