Open bolt delay is a mechanism used in some firearms, particularly machine guns, to control the rate of fire. It works by delaying the closing of the bolt after firing, allowing the spent casing to be ejected and a new round to be chambered before the bolt fully closes. This delay creates a pause between shots, slowing down the rate of fire.
How Open Bolt Delay Works
- Firing: When the trigger is pulled, the firing pin strikes the primer, igniting the round.
- Bolt Opens: The pressure from the expanding gases pushes the bolt back, extracting and ejecting the spent casing.
- Delay: The open bolt design incorporates a delay mechanism, which prevents the bolt from immediately closing. This mechanism can be a spring-loaded plunger, a hydraulic buffer, or a combination of both.
- Chambering: During the delay, the next round is fed into the chamber from the magazine.
- Bolt Closes: Once the delay is over, the bolt slams forward, chambering the new round and preparing the firearm for the next shot.
Advantages of Open Bolt Delay
- Reduced Rate of Fire: The delay slows down the rate of fire, making the weapon more controllable and reducing the risk of overheating.
- Improved Accuracy: The slower rate of fire allows for more precise aiming and shot placement.
- Simplified Design: Open bolt designs are generally simpler and less expensive to manufacture than closed bolt designs.
Disadvantages of Open Bolt Delay
- Increased Cycle Time: The delay increases the time between shots, making the weapon less responsive.
- Increased Sensitivity: Open bolt weapons are more sensitive to dirt and debris, which can interfere with the delay mechanism.
- Potential for Accidental Discharge: In some cases, if the bolt is not fully closed, a round can be chambered without the trigger being pulled, leading to an accidental discharge.
Examples of Open Bolt Firearms
- M16: While the M16 is a closed bolt design, the M16A1 and earlier versions used a delayed blowback system, which incorporates an open bolt delay for the first shot.
- M60: The M60 machine gun is a classic example of an open bolt design with a hydraulic buffer system that delays the bolt's closing.
- MG42: The German MG42 machine gun also utilizes an open bolt design with a spring-loaded plunger for delay.
