What should the shooter do to ensure the magazine is properly seated?

To ensure that the magazine is properly seated in the M9 service pistol, the shooter should push the magazine firmly with the heel of the hand. This action provides the necessary force to fully insert the magazine into the magazine well, allowing the feed lips to align correctly with the chamber feeding mechanism. A securely seated magazine is crucial for reliable feeding during operation.

Ensuring that the magazine is properly seated helps prevent malfunctions such as misfeeds or failures to fire, which can occur if the magazine is not securely locked in place. Pushing it with the heel of the hand maximizes the surface area contacting the magazine, ensuring that it is pushed in fully and securely.

Other actions, like checking the magazine release or shaking the pistol, do not directly ensure the magazine's proper seating. Additionally, rotating the pistol may cause the magazine to unseat rather than secure it. Thus, using the heel of the hand is the most effective technique to make sure the magazine is secure and ready for use.