How the shotgun is fired
A shotgun used for shotshells features a smoothbore barrel, meaning there is no rifling. When a shotshell is fired, the tiny round pellets travel down this smooth bore to the target. The consistency of roundness of each pellet determines how the pellets fly.
Step 1: Shell is loaded into chamber.
Step 2: Action is closed, and the shell is ready to be fired.
Step 3: Firing pin makes contact with primer and causes primer mix to explode in the shell.
Step 4: Rapidly accumulating high pressure from the burning gunpowder pushes projectile out of the barrel.