Which component of the rifle can directly affect its muzzle velocity?

The length of the barrel plays a crucial role in determining the muzzle velocity of a rifle. As a bullet travels through the barrel, it is propelled by the expanding gases produced by the burning gunpowder. A longer barrel allows for a more extended period of acceleration due to these gases acting on the bullet. This increased length gives the bullet more time to gain velocity, resulting in a higher muzzle velocity when it exits the barrel.

Conversely, a shorter barrel restricts the time the bullet can be accelerated, leading to a lower muzzle velocity. Thus, barrel length is a fundamental factor influencing the performance of a rifle, specifically in terms of how fast the bullet travels when it leaves the weapon.

Other components, such as the stock material, trigger mechanism, and sights, do not have a direct impact on muzzle velocity. They may influence factors such as handling, accuracy, and ease of use but do not alter the speed at which a bullet exits the rifle. Therefore, the length of the barrel is the primary factor among the options provided that directly affects muzzle velocity.