What FPS is Subsonic? Understanding Subsonic Velocities in Firearms
The question "What FPS is subsonic?" doesn't have a single definitive answer. Subsonic velocity refers to a projectile's speed being slower than the speed of sound. Because the speed of sound varies depending on factors like air temperature, humidity, and altitude, the exact FPS (feet per second) that constitutes subsonic will also vary.
Understanding the Speed of Sound:
The speed of sound is roughly 1125 feet per second (fps) at sea level and 68°F (20°C). However, this speed can change significantly. Colder air leads to a slightly slower speed of sound, while warmer, more humid air increases it. High altitudes also result in a slower speed of sound. This means a bullet traveling at 1050 fps might be subsonic in colder, higher altitudes but supersonic at sea level on a hot day.
Practical Considerations for Subsonic Ammunition:
For practical purposes, most subsonic ammunition is designed to achieve velocities significantly below the speed of sound to ensure reliable subsonic performance across a range of conditions. Generally, you'll see subsonic ammunition advertised with velocities in the range of 900-1100 fps, but even within that range, variations exist based on cartridge type and manufacturer.
Factors Affecting Subsonic Velocity:
- Cartridge Type: Different cartridges are designed with varying powder charges and projectile weights, resulting in different velocities. A subsonic .22 Long Rifle round will have a much lower FPS than a subsonic .300 Blackout round, for example.
- Projectile Weight: Heavier bullets generally travel slower than lighter bullets with the same powder charge. This is a key design element in subsonic ammunition.
- Powder Charge: The amount of propellant used directly impacts the velocity of the projectile. Subsonic rounds use carefully reduced powder charges to keep velocities below the speed of sound.
- Environmental Conditions: As previously mentioned, temperature, humidity, and altitude all significantly impact the speed of sound and therefore the classification of a bullet as subsonic or supersonic.
Why Subsonic Ammunition is Important:
Subsonic ammunition is crucial in specific applications where reducing noise is critical. Supersonic bullets create a sonic boom, a sharp cracking sound, which is absent with subsonic rounds. This makes subsonic ammo ideal for:
- Hunting: Reduced noise can improve the chances of a successful hunt, especially when hunting wary game.
- Suppressor Use: Suppressors (or silencers) are most effective when used with subsonic ammunition. A supersonic round will still create a significant amount of noise even with a suppressor.
- Tactical Situations: In close-quarters combat or stealth operations, reduced noise is paramount.
In Conclusion:
While a precise FPS value for "subsonic" is variable, aiming for velocities well below 1125 fps—typically in the range of 900-1100 fps—will usually ensure you're using subsonic ammunition. Always check the manufacturer's specifications for the exact velocity of your chosen ammunition under stated conditions to ensure it meets your needs.
