Which part of the M16 and M4 can be adjusted to change the weapon’s length?

The stock is the component of the M16 and M4 that can be adjusted to change the weapon's length. By extending or retracting the stock, a shooter can modify the overall length of the rifle to better suit their physical stature or preferences, enhancing comfort and control during use. This adaptability is crucial for achieving optimal shooting posture and accuracy, as each shooter may require a different configuration based on their specific needs.

The barrel, grip, and sights do not provide a mechanism for altering the length of the weapon in the same way the stock does. The barrel's length is fixed and primarily influences the ballistic performance of the round, while the grip is designed to provide control and stability without affecting the length of the firearm. Sights are focused on aiming and do not have any relation to the weapon's overall length or adjustability.