The .300 AAC Blackout cartridge has earned a dedicated following among shooters and hunters who value versatility and performance. One of its standout features is its subsonic capability, which makes it exceptionally quiet when paired with a suppressor. For enthusiasts looking to maximize their ammunition’s potential while managing costs, reloading presents an attractive option.
Reloading your own .300 Blackout subsonic load data offers numerous advantages beyond simple cost savings. It allows you to tailor loads to your specific firearm, achieve better accuracy, and experiment with different bullet weights and powder charges to find what works best for your needs. Whether you’re a competitive shooter seeking precision or a hunter wanting reliable performance in the field, understanding the reloading process can significantly enhance your shooting experience.
This guide walks you through everything you need to know about reloading .300 AAC Blackout subsonic rounds, from selecting components to fine-tuning your loads for optimal performance.
What is .300 AAC Blackout Subsonic?
The .300 AAC Blackout (also known as 7.62×35mm) was developed by Advanced Armament Corporation in collaboration with Remington Defense. It was designed to provide .30-caliber performance in the AR-15 platform while offering superior ballistics to the 5.56 NATO round, particularly at short to medium ranges.
What makes the .300 AAC Blackout particularly appealing is its ability to function effectively in both supersonic and subsonic configurations. Subsonic loads keep the bullet traveling below the speed of sound (approximately 1,125 feet per second), which eliminates the sonic crack that accompanies supersonic ammunition. When combined with a suppressor, this creates an exceptionally quiet shooting experience ideal for tactical applications, hunting situations where stealth is paramount, or recreational shooting where noise reduction matters.
The cartridge’s popularity has grown steadily since its introduction, thanks to its adaptability and ease of use in existing AR-15 rifles with minimal modifications.
Why Reload .300 AAC Blackout Subsonic?
Cost Savings
Factory subsonic ammunition can be expensive, particularly for premium loads designed for hunting or tactical use. Reloading your own ammunition can reduce costs by 40-60% compared to purchasing factory rounds, especially when you buy components in bulk. Over time, these savings add up considerably, particularly for shooters who practice regularly or participate in competitive events.
Customization Options
Every firearm has unique characteristics, and what works perfectly in one rifle may not perform as well in another. Reloading gives you complete control over your ammunition specifications. You can adjust powder charges, experiment with different bullet weights, and modify seating depths to find the perfect combination for your specific firearm and intended use.
Improved Accuracy and Performance
Factory ammunition is manufactured to work reliably across a wide range of firearms, which means it’s designed to be “good enough” for most guns. By tailoring your loads to your specific rifle, you can often achieve tighter groups and more consistent performance than factory ammunition provides. This level of precision is especially valuable for competitive shooters and hunters who need to make accurate shots at varying distances.
Components Needed for Reloading
Bullets
For subsonic .300 AAC Blackout loads, heavier bullets are essential. Most reloaders use bullets weighing between 190 and 220 grains, with 208-grain and 220-grain projectiles being particularly popular choices. The extra weight helps keep velocities below the sound barrier while maintaining adequate downrange energy.
Bullet design also matters. Boat-tail bullets typically provide better ballistic coefficients, while flat-base designs may be easier to seat consistently. For hunting applications, consider expanding bullets designed for subsonic velocities, as standard bullets may not expand reliably at lower impact speeds.
Cases
Brass quality significantly impacts both safety and performance. .300 AAC Blackout cases can be formed from .223/5.56 brass, but purpose-made .300 Blackout brass is generally preferred for subsonic loads. Look for cases from reputable manufacturers like Starline, Lapua, or Lake City.
Inspect cases carefully for signs of wear, cracks, or excessive stretching. Proper case preparation, including trimming to uniform length, ensures consistent powder capacity and pressure characteristics.
Powder
Powder selection is critical for subsonic loads. You need a powder that burns efficiently at lower pressures while providing consistent velocities. Popular choices for .300 AAC Blackout subsonic loads include:
- H110/W296 (for heavier charges)
- CFE BLK (specifically designed for the .300 Blackout subsonic load data)
- Accurate 1680
- IMR 4227
Each powder has different burn rates and characteristics, so consult reliable reloading data before making your selection. Start with published load data from sources like xxlreloading.com, which offers extensive information for various bullet and powder combinations.
Primers
Standard small rifle primers work well for most .300 AAC Blackout subsonic loads. Some reloaders prefer magnum small rifle primers when using slow-burning powders or in colder temperatures, as they provide more consistent ignition.
Primer selection affects both pressure and velocity, so stick with the primer type specified in your load data. Switching primers requires working back up from minimum loads to ensure safety.
Step-by-Step Reloading Process
Case Preparation
Start by inspecting each case for defects. Clean cases thoroughly using a tumbler or ultrasonic cleaner to remove dirt, carbon buildup, and debris.
Next, resize cases using a full-length sizing die to ensure they’ll chamber properly in your firearm. Lubricate cases lightly before resizing to prevent stuck cases and die damage.
After resizing, trim cases to the specified length (typically 1.368 inches for .300 AAC Blackout). Consistent case length ensures uniform powder capacity and consistent bullet seating depth. Deburr and chamfer case mouths to remove sharp edges that could damage bullets during seating.
Priming
Insert primers carefully using a hand priming tool or press-mounted priming system. Primers should seat flush with or slightly below the case head. Avoid crushing primers, as this can cause dangerous pressure spikes.
Work in a clean, organized environment and handle primers carefully. Store them away from heat sources and powder to prevent accidents.
Powder Charging
Accurate powder measurement is absolutely critical for subsonic loads, where small variations can significantly affect velocity and pressure. Use a quality powder scale or electronic dispenser to measure each charge precisely.
For subsonic loads, you’re typically working with smaller powder charges than supersonic loads, which means there’s more empty space in the case. This can lead to inconsistent ignition if powder doesn’t position consistently. Some reloaders use inert fillers or orient cases consistently during loading to address this issue.
Always double-check your load data and start with minimum charges, working up gradually while monitoring for pressure signs.
Bullet Seating
Set your seating die to achieve the correct overall cartridge length (OAL). For .300 AAC Blackout subsonic loads with heavier bullets, you’ll often seat bullets deeper than you would for supersonic loads to ensure proper function in magazines and chambers.
Many subsonic loads benefit from a slight crimp to ensure consistent powder ignition and to prevent bullet setback during feeding. A taper crimp die works well for .300 Blackout subsonic load data.
Measure several finished rounds to verify consistency in overall length and bullet seating depth.
Crimping
Apply a light to moderate crimp to secure bullets in place. This is particularly important for subsonic loads, as proper bullet hold affects pressure development and velocity consistency.
Too much crimp can deform bullets or cases, while too little may allow bullets to move during feeding or from recoil when firing previous rounds in semi-automatic firearms.
Safety Precautions
Safety must be your top priority when reloading ammunition. Follow these essential guidelines:
- Follow Published Data: Never exceed maximum published loads or experiment with untested combinations. Work up gradually from minimum charges while carefully monitoring for pressure signs like flattened primers, difficult extraction, or excessive case head expansion.
- Wear Protective Gear: Safety glasses protect your eyes from primers or flying debris. Consider hearing protection when using progressive presses or powder measures with audible alerts.
- Maintain Organization: Keep your reloading area clean and organized. Store powders and primers separately and according to manufacturer guidelines. Label everything clearly to prevent dangerous mix-ups.
- Inspect Equipment Regularly: Check dies, presses, and scales periodically for wear or damage. Calibrate electronic equipment according to manufacturer recommendations.
- Focus on the Task: Avoid distractions while reloading. It’s easy to lose count of powder charges or skip steps when your attention wanders.
Tips and Tricks for Accurate Subsonic Loads
Fine-Tuning Powder Charges
Start with published load data and work up in small increments (typically 0.3-0.5 grains for subsonic loads). Test loads at various charge weights to find the optimal balance between velocity, accuracy, and reliable function.
Use a chronograph to verify your velocities stay subsonic. Remember that velocity will vary with barrel length, temperature, and other factors. Build in a safety margin below the sound barrier (aim for 1,000-1,050 fps) to ensure rounds remain subsonic under various conditions.
Experimenting with Bullet Seating Depths
Small changes in seating depth can significantly affect accuracy. Once you’ve found a safe powder charge that delivers subsonic velocities, experiment with seating depth in 0.010-0.020 inch increments to optimize accuracy.
Keep detailed records of your experiments, including powder charge, bullet seating depth, primer type, and results. This information becomes invaluable for future load development and troubleshooting.
Checking for Proper Function
Test new loads in your specific firearm to ensure reliable cycling and feeding. Subsonic loads produce less gas pressure, which can sometimes cause cycling issues in semi-automatic firearms, particularly in the AR-15 platform.
You may need to adjust your gas system or buffer weight to achieve reliable function with subsonic ammunition. Some shooters use adjustable gas blocks to optimize performance with both subsonic and supersonic loads.
Where to Find Reloading Data
Reliable reloading data is essential for safe and effective ammunition. xxlreloading.com stands out as an exceptional resource for handloaders working with .300 AAC Blackout subsonic loads. The platform offers extensive reloading data covering thousands of bullets from various manufacturers, numerous powder types, and hundreds of calibers—all in one convenient location.
What makes xxlreloading.com particularly valuable is its ability to compare performance characteristics of different loads side by side. You can evaluate powder charges, load ratios, pressures, velocities, and even see how loads perform with different barrel lengths. This feature is especially useful for subsonic loads, where precision matters and small changes can significantly impact performance.
The site’s sophisticated ballistics simulator, developed in collaboration with recognized experts, provides accurate predictions based on comprehensive models that account for powder properties, bullet dimensions, and cartridge specifications. All loads in the database have been developed and reviewed by professional staff who regularly add new data.
Additional reputable sources for reloading data include:
- Powder manufacturer manuals (Hodgdon, Alliant, Vihtavuori, etc.)
- Bullet manufacturer load data (Hornady, Sierra, Nosler, Barnes)
- Reloading manuals from Lyman, Lee, and Speer
- The Loadbook series for specific calibers
Always cross-reference data from multiple sources when developing new loads, and never exceed maximum published charges.
Get Started with Your .300 AAC Blackout Subsonic Loads
Reloading .300 AAC Blackout subsonic ammunition combines technical precision with practical craftsmanship. While it requires attention to detail and respect for safety protocols, the rewards are substantial: significant cost savings, ammunition perfectly tailored to your firearm, and the satisfaction of creating your own precision rounds.
Start with quality components, follow published load data carefully, and work up gradually while monitoring for pressure signs. Keep detailed records of your experiments, and don’t hesitate to consult experienced reloaders or online communities when questions arise.
Ready to dive deeper into reloading data for your .300 AAC Blackout subsonic project? Visit xxlreloading.com to access comprehensive load information, compare different powder and bullet combinations, and join a community of fellow handloaders who share your passion for precision ammunition. With over 4 million loads in the database covering thousands of bullets and hundreds of calibers, you’ll find the data you need to develop accurate, reliable subsonic loads for your specific needs.
