What type of bolt mechanism does the M4 use?

The M4 rifle utilizes a closed bolt mechanism, which means the bolt is in a closed position when the weapon is fired. In this system, a round is fed into the chamber and the bolt locks before the shot is fired, allowing for more consistent accuracy and reliability. This design is particularly effective for semi-automatic and fully automatic fire modes since it helps maintain the firearm's performance across different firing conditions and reduces the potential for fouling issues when compared to open bolt designs.

Using a closed bolt system contributes to the overall safety and control of the weapon, as it minimizes the risk of accidental discharges that can occur in open bolt configurations, where the bolt is not locked forward when a round is chambered. This design characteristic is a vital aspect of the M4's functionality, contributing to its effectiveness in various combat scenarios.