Which weapon features a barrel that does not overheat, even after prolonged firing?

The MK19 is a grenade launcher that is known for its ability to sustain prolonged firing without the barrel overheating. This characteristic is largely due to its design, which includes a water-cooled barrel system that dissipates heat efficiently, making it suitable for extended operations without risk of damage or decreased performance caused by heat. In contrast, other weapons listed, such as the M240B, M2, and M16, can experience barrel overheating during sustained fire, which may affect accuracy and functionality. The MK19's cooling capabilities allow it to maintain a high rate of fire over an extended period, making it particularly effective in combat situations where continuous firing may be required.