Understanding Subsonic Loads for .308 Winchester
The Fundamentals of Subsonic Flight
The term “subsonic” refers to projectiles moving below the speed of sound. This speed varies slightly based on atmospheric conditions, but the critical threshold is roughly seven hundred and sixty-seven miles per hour. When a bullet travels slower than this, it doesn’t create the sonic boom characteristic of supersonic projectiles. The absence of this sonic crack is the primary reason for the significantly quieter report associated with subsonic shooting.
The Impact of Speed
The physics of subsonic flight differ from supersonic flight. Supersonic bullets generate a shock wave that can aid in stabilization and maintain a flatter trajectory over distance. Subsonic bullets, conversely, lack this shock wave, which means they are significantly affected by the forces of gravity and wind drift. This means a subsonic .308 bullet will drop much more over distance compared to a supersonic load and may require more precise range estimation and bullet drop compensation.
Bullet Weight Considerations
The critical aspect of subsonic .308 loading is selecting the right bullet weight. Due to the lowered velocity, you need a heavier bullet to maintain sufficient kinetic energy at the target. Lighter bullets lose energy quickly at subsonic speeds. Bullet weight becomes increasingly important. A heavier bullet delivers more energy upon impact. A suitable range of bullet weights for .308 subsonic loads typically starts around two hundred grains and can extend to two hundred and twenty grains, or even beyond. Some shooters experiment with even heavier bullets for specialized applications, though this often requires specific barrel twist rates and careful load development.
Bullet Construction and Applications
Bullet construction is another critical consideration. Expanding bullets are favored for hunting, as they are designed to deliver maximum terminal performance by expanding upon impact. Non-expanding bullets, such as those used for target shooting, are designed to retain their shape and penetrate deeply. Choose the bullet construction that best matches your intended application.
Powder Selection
Powder selection is crucial for subsonic loads. You must use a fast-burning powder to achieve consistent velocities and safe pressures. The goal is to achieve the desired velocity within a safe pressure range. Some examples of powders commonly used for subsonic .308 loads include Hodgdon Trail Boss, IMR 4227, Accurate 5744, and others specifically designed for reduced loads. Carefully consult reloading manuals and online resources for powder load data, and always start with the minimum recommended powder charge. This approach minimizes the risk of exceeding pressure limits and damaging your firearm or causing injury.
Case Selection and Preparation
Case selection involves more than simply using .308 Winchester cases. Preparation is key. Inspect all cases thoroughly before reloading, discarding any that show signs of wear, damage, or corrosion. Case trimming to a uniform length is critical for consistent neck tension and optimal accuracy. A uniform crimp, if applied, can also contribute to consistency. Case preparation also includes cleaning and priming cases.
Primer Selection Guide
Choosing the correct primer is also essential. Standard large rifle primers are generally suitable, but you might consider magnum primers with some slower-burning powders or for colder weather conditions. Consult your reloading manual and the powder manufacturer’s recommendations to ensure proper primer selection for the powder you are using.
Safety First: Essential Precautions for Handloading
The Dangers of Handloading
Handloading is an inherently dangerous activity. This guide provides information for educational purposes only. Always prioritize safety. There are severe risks involved with handloading, and you must be prepared to take those risks seriously. Handloading improperly can result in serious injury or even death, as well as damage to your firearm.
Safe Starting Procedures
Always begin with the *minimum* recommended load listed in a reliable reloading manual or from a reputable source. Do not increase the powder charge unless you are certain it is safe to do so. Work up your loads in small, carefully measured increments, inspecting each round for signs of excessive pressure, such as flattened primers, difficult bolt opening, or ejector marks on the case head.
Pressure Limits
Never exceed the *maximum* load specified in a reloading manual. Overloading can lead to catastrophic firearm failure, causing severe injury or even death.
Inspection Guidelines
Carefully inspect each completed round before firing. Check for proper bullet seating depth, ensuring the bullet is seated firmly but not too deeply. Inspect the case mouth for a proper crimp (if applicable), ensuring the bullet is securely held in place. Look for any cosmetic defects, such as dents or scratches, which may compromise performance.
Working Environment
Always handload in a well-ventilated area. Fumes from the powder and primers can be harmful.
Protective Gear
Always wear safety glasses and hearing protection when handloading and shooting.
Powder and Load Mixing
Never mix different powders or loads. This is a recipe for disaster. Using the wrong powder or mixing powders can lead to dangerous pressure spikes.
Firearm Maintenance
Thoroughly clean and inspect your firearms regularly, especially before and after handloading. Make sure your firearm is in good working order and free from obstructions.
Awareness of Hazards
Be acutely aware of the potential for squibs and double-charged loads. A squib load occurs when a bullet becomes lodged in the barrel. A double-charged load involves loading an excessive amount of powder, resulting in dangerously high pressures.
Best Practices
*One* round at a time is the best approach to handloading. This helps minimize potential for mistakes.
.308 Subsonic Load Data (Disclaimer: This is a Starting Point)
Important Safety Notice
This is for informational purposes only. Always consult a reputable reloading manual and work up loads with extreme care. This data is a *starting point* and should not be considered a definitive guide. Start at the lowest charge and work up. Always prioritize safety.
Hodgdon Trail Boss Load Data
Bullet Weight: Two hundred and twenty grain
Powder Charge: Starting at 10.0 grains (minimum) and working up in small increments to a maximum of 11.0 grains.
Primer: Standard Large Rifle Primer
Case: .308 Winchester, trimmed to a uniform length
Overall Length: 2.800 inches
Estimated Velocity: 1000-1050 feet per second
Notes: This is a very low-pressure load, making it suitable for bolt-action rifles. Consider a suppressor. Check for stability.
IMR 4227 Load Data
Bullet Weight: Two hundred and twenty grain
Powder Charge: Starting at 14.0 grains (minimum) and working up to a maximum of 15.0 grains.
Primer: Standard Large Rifle Primer
Case: .308 Winchester, trimmed to a uniform length
Overall Length: 2.800 inches
Estimated Velocity: 1020-1070 feet per second
Notes: Check for signs of pressure. Consider suppressor use. Verify bullet stability.
Accurate 5744 Load Data
Bullet Weight: Two hundred and twenty grain
Powder Charge: Starting at 18.0 grains (minimum) and working up to a maximum of 19.0 grains.
Primer: Standard Large Rifle Primer
Case: .308 Winchester, trimmed to a uniform length
Overall Length: 2.800 inches
Estimated Velocity: 1010-1060 feet per second
Notes: Consult loading data before using. These are starting points and pressure can develop quickly.
Shooting and Performance Considerations
Advantages of Subsonic Loads
The primary benefit of subsonic loads is noise reduction. The absence of a sonic boom makes these loads much quieter than standard supersonic ammunition. Subsonic loads, when used with a suppressor, provide exceptional noise suppression.
Trajectory and Compensation
The reduced velocity of subsonic rounds will also impact bullet trajectory. Subsonic bullets experience significantly greater bullet drop and increased wind drift compared to supersonic projectiles. Be prepared to compensate for these effects by using a ballistic calculator or by sighting your rifle accordingly.
Suppressor Considerations
Suppressor use enhances the quietness of subsonic shooting, but be sure to use a suppressor designed for the .308 Winchester. Make sure the barrel has proper threading for the suppressor. The barrel’s twist rate is essential for stabilizing heavier subsonic bullets. Most .308 barrels will handle the common bullet weights but check the bullet’s twist rate recommendations.
Testing and Refining
Test and tune your loads carefully. Start by firing a series of rounds at a target, noting the impact points. Use a chronograph to measure the velocity of your loads. Analyze the velocity and compare it to your estimated velocity. The chronograph will provide valuable information.
Troubleshooting Common Issues
Keyholing Explained
Keyholing, where the bullet tumbles in flight, is a common problem with subsonic loads. This is typically due to insufficient bullet stabilization, often caused by a barrel with a slow twist rate or a bullet that is not properly matched to the twist rate. If you experience keyholing, consider using a lighter bullet or a faster twist rate barrel.
Cycling Problems
Semi-automatic rifles may experience cycling issues with subsonic loads. This is because subsonic loads generate less energy, which may not be enough to reliably cycle the action. To resolve this, consider using a heavier buffer, an adjustable gas system, or a specialized bolt carrier group to aid cycling.
Other Potential Problems
Other problems may include extraction difficulties, failure to fire, or poor accuracy. Examine your spent cases for any indications of excessive pressure, such as flattened primers or case head expansion. Ensure your rifle is properly maintained.
Conclusion
The Quiet Path
Subsonic shooting with the .308 Winchester offers a unique and rewarding shooting experience. It is essential to approach handloading subsonic ammunition with patience, attention to detail, and the utmost respect for safety. Always prioritize your safety.
The Value of Customization
Handloading allows for customization. However, it requires diligence. By understanding the principles of subsonic ballistics, meticulously following safe loading practices, and carefully testing your loads, you can achieve remarkable results.
Final Reminder
Responsible handloading is critical. If you have any doubts, seek assistance from experienced reloaders. If you have questions, consult a professional. If anything feels unsafe, stop and get help.
Additional Resources
Hodgdon Reloading Data Center: ([Link to Hodgdon’s reloading data])
IMR Powders: ([Link to IMR’s website])
Accurate Powders: ([Link to Accurate’s website])
Reloading Forums: (Search on reloading forums)
