Which part is included in the barrel assembly of the M240?

The barrel assembly of the M240 includes the gas regulator, which is a critical component for managing the operation of the weapon. The gas regulator controls the amount of gas extracted from the propellant gases during firing, which in turn affects the cycling of the action and the overall functioning of the machine gun. Proper adjustment of the gas regulator is essential for reliable operation, especially in different environmental conditions and with various types of ammunition.

In contrast, the other components listed are related to the overall functioning of the firearm but do not form part of the barrel assembly. The extracted collar serves a different functionality during the ejection of spent casings, the chamber lock relates to the integrity of the chamber during firing, and the cooling sleeve, while important for heat dissipation, is not part of the essential components located within the barrel assembly itself. Hence, the gas regulator is identified as the correct part included in the barrel assembly of the M240.