The question of whether a .350 Legend upper receiver will fit a 5.56 NATO lower receiver is a common one among AR-15 enthusiasts. The short answer is: generally, no. While both calibers utilize the AR-15 platform, crucial differences prevent direct compatibility. This article will delve into the specifics, explaining why this isn't possible and exploring the potential consequences of attempting such a combination.
Understanding AR-15 Receiver Compatibility
The AR-15 platform's modularity is a key strength, allowing for easy caliber changes through upper receiver swaps. However, this interchangeability has limits. The lower receiver, housing the fire control group and magazine well, is largely caliber-independent. However, the upper receiver, containing the barrel, bolt carrier group (BCG), and charging handle, is heavily caliber-specific.
Key Differences Between .350 Legend and 5.56 NATO
The incompatibility stems from several key differences between the .350 Legend and 5.56 NATO cartridges:
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Caliber: The most obvious difference is the cartridge diameter. The .350 Legend has a significantly larger diameter than the 5.56 NATO round. This immediately rules out using a .350 Legend barrel in a 5.56 NATO upper.
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Bolt Face: The bolt face, the part of the bolt that engages the cartridge case, is designed specifically for each caliber. A .350 Legend bolt face is larger than a 5.56 NATO bolt face and will not function correctly with a 5.56 NATO casing. Attempting to force it could result in catastrophic failure.
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Barrel Dimensions: The .350 Legend barrel has a larger bore diameter and a different rifling twist rate compared to a 5.56 NATO barrel. This difference is critical for proper bullet stabilization and accuracy.
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Magazine Well: While the lower receiver itself might be compatible, the magazines are not interchangeable. A .350 Legend magazine will not fit into a 5.56 NATO lower receiver.
Potential Dangers of Forcing Compatibility
Attempting to force a .350 Legend upper onto a 5.56 lower receiver is extremely dangerous and should never be attempted. The following are potential outcomes:
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Bolt Failure: The oversized .350 Legend bolt will not properly engage the 5.56 NATO casing, leading to potential malfunction and possible catastrophic failure.
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Barrel Damage: The .350 Legend bullet will not properly fit the 5.56 NATO barrel, leading to potential damage to the barrel and causing dangerous pressures to build.
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Receiver Damage: The pressure from the mismatched components could damage the upper and lower receivers beyond repair.
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Personal Injury: In the worst-case scenario, a failure could result in serious injury or even death to the shooter.
Alternatives for Using .350 Legend
Instead of trying to force compatibility, consider these alternatives:
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Purchase a dedicated .350 Legend lower receiver: Several manufacturers offer lower receivers specifically designed for the .350 Legend. These will ensure proper fit and function.
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Build a complete .350 Legend AR-15: This allows you to choose all components designed to work together, eliminating the risk of incompatibility.
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Stick with your current 5.56 NATO setup: If you enjoy your 5.56 NATO AR-15, there is no need to change calibers.
Conclusion: Safety First
The compatibility issue between .350 Legend uppers and 5.56 NATO lowers is not a matter of simple modification. The inherent design differences pose serious safety risks. Prioritizing safety and purchasing compatible components is crucial for responsible firearm ownership. Never attempt to force incompatible parts together, and always prioritize safety when handling firearms.