Why should the barrel of an M240 be changed after it becomes too hot?

Changing the barrel of an M240 after it becomes too hot is crucial for several reasons, primarily to guard against cook-offs and increase the life of the barrel. When a firearm is fired continuously, the heat generated can cause the ammunition to ignite prematurely, leading to a cook-off. This is a dangerous situation where a round may fire without the trigger being pulled, potentially causing injury to the operator or bystanders.

Furthermore, excessive heat can lead to accelerated wear and tear on the barrel. The structural integrity of the barrel can be compromised under high temperatures, which can reduce its effectiveness over time. By regularly changing the barrel when it becomes too hot, the operator ensures not only the safety of their operation but also prolongs the life of the weapon, maintaining its readiness and reliability for future use. This practice is a standard procedure in machine gun operation to ensure consistent performance and safety.