What step in firing a shotgun shell involves the action being closed?

The step in firing a shotgun shell where the action is closed is when the shell is loaded into the chamber. This process involves ensuring that the shotgun is ready to fire; the action must be fully closed to secure the shell in place and allow the mechanism to operate correctly. When the action is closed, it also means that the firing pin is positioned to strike the primer of the shell when the trigger is pulled, facilitating the discharge of the firearm.

Loading the shell is an essential step in ensuring that the firearm is ready for use, as no shot can be fired if the shell is not correctly seated in the chamber. Other options do not relate to the action being closed in the same way, as pulling the trigger is a separate action that comes after the shell is loaded and the action is closed. Similarly, pushing the projectile into the barrel is not a step taken with a shotgun, and preparing the firing pin occurs as a mechanism of the action being closed rather than a standalone step. Thus, loading the shell into the chamber clearly represents the moment when the action of the shotgun is closed, making it the correct answer.