While there is no oxygen in space to support combustion, gun cartridges contain their oxidizer, typically composed of chemicals like potassium nitrate or lead styphnate. These elements produce oxygen when ignited, allowing the propellant contained in the cartridge to burn and generate the necessary pressure to expel the bullet. As a result, the gun will function similarly in space as it would on Earth, with the exception of the sound produced by the shot, which would be different due to the absence of an atmosphere.