The .40 Smith & Wesson cartridge, a popular choice in law enforcement and civilian self-defense, has found its way into the AR-15 platform, albeit through conversion. This isn't a standard caliber for AR uppers; therefore, understanding the nuances of a 40 cal AR upper is crucial before committing to a purchase. This guide dives deep into the specifics, covering conversions, considerations, and the overall capabilities of this unique setup.
Understanding the 40 Cal AR Upper Conversion
Unlike standard 5.56 NATO or .223 Remington uppers, a .40 S&W AR upper requires a conversion. This generally involves replacing the bolt carrier group (BCG), barrel, and potentially the magazine well to accommodate the larger cartridge. This conversion isn't always straightforward and requires careful consideration of several factors.
Key Components of the Conversion:
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Barrel: A .40 S&W barrel is significantly different from a 5.56mm barrel, featuring a larger bore and chamber. Choosing a high-quality barrel is paramount for accuracy and reliability.
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Bolt Carrier Group (BCG): The BCG must be specifically designed for the .40 S&W cartridge and properly sized for reliable function. Using the wrong BCG can lead to malfunctions and potentially damage the firearm.
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Magazine Well: Depending on the conversion kit, the magazine well might need modification or replacement to accommodate the different magazine shape and size.
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Magazines: .40 S&W AR magazines are readily available, but their capacity is often lower than standard AR magazines.
Considerations Before Purchasing a 40 Cal AR Upper
Before investing in a 40 cal AR upper, several crucial factors need careful consideration:
Reliability and Function:
While reliable .40 S&W AR uppers exist, they aren't always as robust as their 5.56 counterparts. The larger cartridge can put more stress on the components, potentially leading to malfunctions if not properly maintained and assembled. Reputable manufacturers and meticulous attention to detail are essential for ensuring reliability.
Accuracy:
Accuracy can be a concern with .40 S&W AR uppers, often less precise than standard AR calibers. Barrel quality and ammunition selection significantly impact accuracy, so choosing a high-quality barrel and consistent ammunition is crucial.
Cost:
Conversion kits and complete uppers for .40 S&W are generally more expensive than standard AR uppers. The specialized components and lower production volume contribute to this higher cost.
Availability of Parts and Ammunition:
While .40 S&W ammunition is widely available, it might not be as ubiquitous or affordable as 5.56 NATO or .223 Remington. Similarly, finding replacement parts for a .40 S&W AR upper might require more searching than for standard calibers.
Capabilities and Applications of a 40 Cal AR Upper
Despite the challenges, a 40 cal AR upper offers some unique capabilities:
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Stopping Power: The .40 S&W cartridge delivers significantly more stopping power than 5.56 NATO, making it a more effective choice for self-defense or home defense scenarios where stopping power is prioritized.
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Reduced Recoil (Compared to Larger Calibers): While more significant than 5.56 NATO, the recoil is still manageable for most shooters, providing a more controlled shooting experience compared to larger pistol calibers in an AR platform.
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Versatility: Although not as widely supported as other calibers, some versatility can still be achieved within the AR-15 platform itself; swapping uppers provides an option to use multiple calibers on the same lower receiver.
Conclusion
A 40 cal AR upper presents a unique niche within the AR-15 world. While it offers greater stopping power compared to standard calibers, it’s crucial to weigh the potential downsides of reliability, cost, and accuracy concerns before making a purchase. Thorough research, selecting reputable manufacturers, and prioritizing proper maintenance are critical for a successful and enjoyable shooting experience. This guide offers a starting point for your research, but independent verification and expert consultation are always recommended before modifying or purchasing any firearm.
