The bullet grain weight does have an effect on the speed (velocity) of the bullet, but it is not a direct correlation. Generally, a heavier bullet will have a lower velocity compared to a lighter bullet when fired from the same firearm.
Here's how the bullet grain weight affects speed:
Powder Charge: The velocity of a bullet is primarily determined by the amount of gunpowder (propellant) used in the cartridge. The powder charge is tailored to provide optimal performance for a specific bullet weight. Manufacturers develop specific loadings for different bullet weights to achieve the desired velocity and ballistic characteristics.
Pressure and Barrel Length: The pressure generated inside the firearm's chamber when the cartridge is fired also affects the velocity. Heavier bullets typically generate higher pressures due to the increased resistance encountered while traveling down the barrel. Additionally, barrel length plays a role in determining the velocity. A longer barrel generally allows for a more complete burn of the propellant, resulting in higher velocities.
Ballistic Coefficient: The bullet's shape and design, which contribute to its ballistic coefficient (BC), can also impact its velocity. A higher BC bullet will experience less air resistance and retain its velocity better than a bullet with a lower BC. Therefore, bullets with higher BC tend to maintain their speed over longer distances.
It's important to note that the velocity of a bullet is also influenced by other factors, such as the firearm's barrel twist rate, environmental conditions (e.g., temperature, altitude), and the specific propellant used. Therefore, it's crucial to consult manufacturer data, reloading manuals, or ballistics charts for the specific bullet and cartridge combination to get accurate velocity information.
Choosing the appropriate bullet weight for a particular application depends on various factors, including the intended purpose (e.g., self-defense, target shooting, hunting), desired terminal performance, and firearm characteristics. It's recommended to consult with experts, such as firearm instructors or ammunition manufacturers, for guidance on selecting the appropriate bullet weight and load for your specific needs.