Which of the following is NOT a type of firearm action?

In the context of firearm actions, it's important to understand the specific mechanisms by which firearms operate. Lever, revolving, and pump are all recognized types of firearm actions.

The lever action involves a lever that is operated to load and eject cartridges, as commonly seen in certain rifles. The revolving action, typical of revolvers, features a rotating cylinder that holds multiple cartridges and aligns them with the barrel as they are fired. The pump action utilizes a sliding fore-end to cycle rounds into the chamber and eject spent cartridges, which is a common mechanism in shotguns.

On the other hand, "automatic" is not a specific type of firearm action but rather a classification that describes how a firearm operates. Automatic firearms can refer to any firearm that automatically reloads after each shot, which can include semi-automatic (fires one bullet per trigger pull) and fully automatic (fires continuously as long as the trigger is held). Therefore, the term "automatic" does not represent a distinct action mechanism like the others do, making it the correct choice in this context.