The .450 Bushmaster is quickly gaining popularity among hunters and enthusiasts seeking a powerful round for close-to-medium range applications. Its substantial stopping power makes it ideal for hunting larger game, while its manageable recoil makes it a viable option for AR-15 platform builds. This guide will walk you through building a reliable and accurate .450 Bushmaster AR-15, covering everything from parts selection to final assembly.
Choosing the Right Lower Receiver
The lower receiver is the foundation of your AR-15 build, and choosing the right one for a .450 Bushmaster is crucial. While a standard AR-15 lower will technically work, it's not recommended. The higher pressures generated by the .450 Bushmaster round necessitate a lower receiver specifically designed to handle them. Look for lowers explicitly marked as compatible with the .450 Bushmaster, ensuring they are made from high-quality materials like forged 7075-T6 aluminum. Never use a standard AR-15 lower receiver with a .450 Bushmaster upper.
Key Considerations for Lower Receivers:
- Material: Forged 7075-T6 aluminum is the industry standard for durability.
- Compatibility: Ensure the lower is explicitly rated for .450 Bushmaster.
- Manufacturer Reputation: Choose a reputable manufacturer known for producing high-quality parts. Brands like Aero Precision, PSA, and others offer quality .450 Bushmaster compatible lowers.
Selecting the Upper Receiver and Barrel
The upper receiver and barrel are the heart of your .450 Bushmaster AR. The barrel is where the magic happens, and choosing the wrong one can lead to accuracy issues and potential safety hazards.
Barrel Selection:
- Length: 16-inch barrels are common, offering a good balance of velocity and maneuverability. Shorter barrels are also available but will result in a noticeable velocity reduction.
- Twist Rate: A 1:20 twist rate is generally recommended for the .450 Bushmaster, providing optimal stabilization for heavier bullets.
- Material: 4140 chrome moly vanadium steel is a popular choice for its durability and accuracy.
- Profile: A heavier profile barrel will reduce barrel whip and improve accuracy, while a lighter profile will reduce weight.
Upper Receiver Considerations:
- Material: Forged 7075-T6 aluminum is again the preferred material for its strength and durability.
- Compatibility: Make sure the upper receiver is specifically designed for .450 Bushmaster. It needs to be able to handle the increased pressures.
- Forward Assist and Ejection Port: The .450 Bushmaster's larger cartridge might require modifications to the ejection port for reliable cycling. Always check the manufacturer's specifications.
Bolt Carrier Group (BCG) and Buffer System
The BCG and buffer system are critical for reliable cycling. Using a standard AR-15 BCG is a recipe for malfunction, potential damage, and even injury.
BCG Considerations:
- .450 Bushmaster Specific: A BCG designed for the .450 Bushmaster is non-negotiable. These BCGs are typically heavier and more robust to handle the increased pressures. Look for nitride or other hard-coat finishes for enhanced durability.
- Material: Look for high-quality materials like Carpenter 158 steel.
- Manufacturer: Choose a reputable manufacturer with a proven track record of producing reliable BCGs.
Buffer System:
- Heavier Buffer: A heavier buffer is necessary to manage the recoil of the .450 Bushmaster round. A standard AR-15 buffer will likely lead to malfunctions. Experimentation may be needed to find the optimal weight for your specific build.
- Buffer Spring: A stronger buffer spring will complement the heavier buffer, ensuring reliable cycling.
- Buffer Tube: While a standard buffer tube might work, many builders prefer a thicker, more robust tube for added strength.
Gas System and Other Components
- Gas Block and Tube: A low-profile gas block is usually preferred, and you'll need a gas tube designed for the .450 Bushmaster.
- Handguard: A free-floating handguard is highly recommended to ensure accuracy. M-LOK and KeyMod systems offer numerous attachment points for accessories.
- Trigger: Choose a trigger that suits your shooting style and preferences. While many triggers are drop in, ensure that it's compatible with the lower receiver and its firing pin.
- Magazines: .450 Bushmaster magazines are readily available from various manufacturers. Capacity varies, so consider your intended use case.
Assembling Your .450 Bushmaster AR
Once you've gathered all the necessary parts, assembling your .450 Bushmaster AR is a straightforward process, though some familiarity with AR-15 assembly is helpful. Numerous detailed guides and videos are available online if you need assistance. Always ensure the weapon is unloaded and clear before assembling or disassembling any firearm.
Safety Precautions
- Always follow safe gun handling practices.
- Never point the firearm at anything you don’t intend to shoot.
- Keep your finger off the trigger until ready to fire.
- Ensure the weapon is unloaded before any assembly, cleaning, or maintenance.
- Wear appropriate eye and ear protection when shooting.
Building a .450 Bushmaster AR is a rewarding experience, but it requires careful planning and selection of compatible parts. Prioritize safety and quality throughout the entire process. Remember to consult relevant state and local laws regarding firearm ownership and use before undertaking this project.