sentence: Gun powder is packed into metal cylinders behind the bullet, called the cartridge.
sentences_before: It burns very rapidly, and creates gases. Those gases use up more space than the gunpowder they come from, so they push outward. If the gunpowder is in a small space, the gasses will push on the walls of the space, building up pressure. A bullet  is pushed on in this way inside of a gun, causing it to fly out at high speeds.
concept_name: gun powder
headings: Gunpowder
categories: Firearms