What component contains heat-resisting inner shields in the M16A3/M4A1 service rifle?

The hand guard in the M16A3/M4A1 service rifle is designed to protect the user from heat generated during firing. It contains heat-resisting inner shields that are specifically engineered to dissipate heat and prevent the operator from burning their hands when the firearm is used continuously or in rapid succession. This feature is crucial for maintaining the rifle's usability and safety, especially in scenarios where prolonged firing may occur. The materials and design of the hand guard play a significant role in effective heat management, thus allowing the shooter to maintain control and comfort while using the rifle.

In contrast, the upper receiver primarily houses the bolt carrier group and may contribute to the overall structural integrity of the rifle, while the lower receiver contains the trigger mechanism and magazine well but does not provide heat shielding. The magazine group assembly is focused on feeding rounds into the chamber and does not involve heat-resisting components either.