Why a gun can fire without air
A conventional firearm does not need the surrounding atmosphere to supply oxygen. The key is inside each cartridge: its propellant includes both fuel and an oxidizer, a chemical that helps the fuel react. When the firing pin strikes the primer, that small ignition charge starts the propellant burning.
Burning produces hot, rapidly expanding gas. In the confined space of the cartridge and barrel, the gas pressure drives the bullet forward and out of the muzzle. The reaction is self-contained, so a vacuum outside the gun does not prevent the shot.
What changes in space
On Earth, a gunshot’s sharp report reaches a listener as pressure waves traveling through air. A vacuum has no air to carry those waves, so a nearby person outside the firearm would not hear the shot through open space. The gun’s moving parts could still vibrate, and sound could travel through a solid structure they touched—but not across the vacuum itself.
The bullet also does not need air to keep moving. Once launched, it continues along its path unless gravity or another force changes that motion. With little or no atmosphere to slow it, it would not lose speed to air resistance as it does on Earth. The shot is possible because the chemistry travels with the ammunition; the silence is a consequence of the missing air.
