Firing a shotshell is a physical and chemical chain reaction that takes place in a split second.
- The firing pin strikes the primer, igniting the primer compound.
- The flame ignites the powder charge, which burns rapidly, creating a high volume of gases.
- The gases under pressure will expand to the muzzle, seeking the least resistant path to expansion.
- Because the wad and shot are between the gases and the muzzle, the gases push the shot and wad along.