Which of the following is NOT a determination of a hot barrel for the 240?

The determination of whether a machine gun barrel is considered "hot" is critical for safety and operational effectiveness. A hot barrel typically results from excessive firing, which can lead to overheating and potential damage.

In this context, declaring a barrel as hot often relies on specific indicators and action durations. The correct option states that "less than 15 mins since last deemed hot" is not a determination of a hot barrel. This is accurate because a barrel being considered "hot" is usually based on direct firing activities rather than a time-based assessment after it has been designated as hot. If a barrel has been fired heavily—through a certain number of rounds in a brief timeframe or continuous firing—it can be deemed hot; however, simply waiting for a period of less than 15 minutes does not automatically imply it remains hot.

The other choices, such as the number of rounds fired in a short duration or being assessed by a team leader or vehicle commander, directly relate to the physical and operational signs of overheating in a barrel.