Which of the following weapons fire from a closed bolt?

The M4 rifle operates from a closed bolt, which means that the bolt is fully closed when the weapon is fired. This design contributes to increased accuracy and enhanced safety during rapid fire situations. In a closed-bolt system, the round is chambered and the firing pin is not exposed until the trigger is pulled. This allows for better heat management and reduces the chance of an accidental discharge or cooking off of a round due to heat buildup, as the round stays chambered securely in the closed bolt position until action is taken to fire it.

In the context of the other weapons listed, the 240B and M249 SAW both utilize a gas-operated, open bolt firing mechanism, where the bolt is held open after firing, allowing for better cooling and easier recoil management during sustained fire. The MK19 grenade launcher also operates from an open bolt, which enhances safety by preventing the inadvertent ignition of ammunition under certain conditions. Understanding the operational mechanics of these weapons helps in comprehending their effective use and design intentions in various tactical scenarios.