What component is checked by squeezing the trigger to perform a double-action check?

Squeezing the trigger to perform a double-action check primarily involves the hammer. In a double-action firearm, pulling the trigger initiates a sequence that both cocks and releases the hammer. This means that by squeezing the trigger, the shooter can confirm that the hammer moves to the rear and is able to fall forward when the trigger completes its pull. This action is crucial, as it ensures the firearm is functional and ready to fire. Additionally, it serves as a check for the trigger mechanism, as any obstructions or malfunctions should be noticeable during this process.

In contrast, the other components listed do not directly relate to the operation confirmed by squeezing the trigger in a double-action check. For example, the slide stop affects the slide's ability to lock back after the last round, while the firing pin block is a safety mechanism preventing the firing pin from striking the cartridge unless the trigger is fully depressed. The magazine catch pertains to the loading and unloading of ammunition and does not play a role in the double-action sequence.