Which component in ammunition acts to prevent gas from escaping?

The wad in ammunition serves the essential purpose of preventing gas from escaping during firing. When a round is discharged, the combustion of gunpowder generates high-pressure gas. The wad acts as a barrier that seals the space between the powder charge and the shot or bullet, ensuring that the gas is contained. This containment is crucial for maximizing the efficiency of the propulsion force that drives the projectile forward.

While the case also plays a role in containing the gases, it primarily serves as the outer casing that holds all components together, including the primer and powder. The projectile is the actual object being fired, and the primer is responsible for igniting the powder charge. However, it is the wad that specifically addresses the issue of preventing gas from escaping. In shotgun shells, for example, the wad can also help to protect the shot or slug and improve accuracy by ensuring a consistent seal.