What type of mechanism does the M16A3 service rifle use?

The M16A3 service rifle employs a gas-operated mechanism, specifically utilizing the direct impingement system. In this design, gases from the fired cartridge are directed from the gas port in the barrel directly into the receiver. This gas flows back into the bolt carrier group, which is then driven backward to cycle the action and eject the spent cartridge casing, chambering a new round from the magazine in the process.

This mechanism is known for its ability to provide a lightweight and relatively simple operation, which contributes to the overall effectiveness and reliability of the rifle. Other operating systems like piston-operated or recoil-operated mechanisms introduce additional components or complexity, which can affect the overall weight and maintenance requirements. Understanding the gas-operated mechanism is essential for grasping how the M16A3 functions, as it directly influences the rifle's performance and handling characteristics during firing and subsequent cycles.