What is the key difference between the sustained and rapid rate of fire for the M240?

The key difference between the sustained and rapid rate of fire for the M240 is indeed the duration of bursts. The sustained rate of fire is designed for prolonged engagements, allowing the weapon to fire at a lower cyclic rate, incorporating 4 to 5 rounds per burst with a pause for barrel cooling, typically firing no more than 100 rounds per 10 minutes. This method helps prevent overheating and ensures greater accuracy over time.

In contrast, the rapid rate of fire allows for shorter bursts with very little cooling time, enabling fire at a higher cyclic rate. This is typically utilized in situations where immediate suppression of enemy fire is necessary. Thus, while both rates address different operational needs, the sustained and rapid distinctions hinge primarily on how long and how quickly rounds are discharged, which directly impacts weapon performance and longevity in combat scenarios.