350 Legend BCG vs. 5.56 BCG: Understanding the Differences
The world of AR-15 rifles offers a wide range of calibers, each with its own unique purpose and performance characteristics. Among these, the .223/5.56 NATO and the .350 Legend stand out as popular choices. When building or modifying an AR-15, a crucial component to consider is the bolt carrier group (BCG). A common question arises: Is a 350 Legend BCG the same as a 5.56 BCG? The answer, while seemingly simple, requires a nuanced understanding of the cartridges and the components that ensure reliable firearm operation. This article delves into the specifics of the 350 Legend BCG versus the 5.56 BCG, exploring their similarities, differences, and implications for AR-15 builds.
Bolt Carrier Group Basics
Before diving into the specifics of the 350 Legend BCG and 5.56 BCG, it’s essential to understand what a BCG is and its function within an AR-15. The BCG is a complex assembly of parts that cycles the action of the rifle. It performs several critical functions:
- Stripping a new round from the magazine.
- Chambering the round.
- Locking the bolt into the barrel extension.
- Firing the round.
- Extracting the spent casing.
- Ejecting the spent casing.
- Cocking the hammer.
The BCG consists of several key components, including the bolt, bolt carrier, gas key, firing pin, and cam pin. Each component plays a vital role in the reliable operation of the rifle.
Similarities Between 350 Legend and 5.56 BCGs
At first glance, a 350 Legend BCG and a 5.56 BCG may appear identical. Both are designed to fit within the AR-15 platform and perform the same basic functions. Many of the individual components are indeed interchangeable. For example, the firing pin, cam pin, and bolt carrier itself are often the same between the two. This commonality stems from the fact that both cartridges are designed to function within the AR-15’s operating system.
The external dimensions of the bolt carrier are generally the same, allowing both BCGs to fit within the upper receiver of an AR-15. This means that the overall weight and balance of the rifle will not be significantly affected by switching between the two.
Key Differences: The Bolt Face
The primary difference between a 350 Legend BCG and a 5.56 BCG lies in the bolt face. The bolt face is the recessed area on the bolt that supports the base of the cartridge. Because the .350 Legend and 5.56 NATO cartridges have different dimensions, their respective bolt faces must also differ.
The .350 Legend cartridge has a larger case head diameter than the 5.56 NATO cartridge. Consequently, the bolt face of a 350 Legend BCG is wider than that of a 5.56 BCG. Attempting to use a 5.56 BCG with a .350 Legend cartridge (or vice versa) will likely result in failure to feed, failure to extract, or other malfunctions. The cartridge simply won’t seat correctly against the bolt face, preventing proper ignition and cycling of the action.
Why the Difference Matters
Understanding the difference in bolt face dimensions is crucial for ensuring the safe and reliable operation of your AR-15. Using the wrong BCG can lead to several problems:
- Failure to Feed: The cartridge may not properly align with the chamber, preventing the bolt from closing completely.
- Failure to Extract: The extractor, which is responsible for pulling the spent casing from the chamber, may not be able to engage the rim of the cartridge properly.
- Damage to the Firearm: Forcing a cartridge into a chamber with the wrong BCG can damage the bolt, barrel extension, or other components.
- Safety Concerns: Malfunctions can create unsafe conditions, potentially leading to injury.
Therefore, it’s imperative to use the correct BCG for the cartridge you intend to fire. Always double-check the markings on your BCG to ensure it is compatible with your chosen caliber.
Identifying a 350 Legend BCG
While some manufacturers may mark their BCGs specifically for the .350 Legend, others may not. If your BCG is not clearly labeled, there are a few ways to identify it as a 350 Legend BCG. The most reliable method is to measure the bolt face diameter. Compare the diameter to specifications online for the 350 Legend BCG and the 5.56 BCG. Another option is to compare it visually to a known 5.56 BCG. The 350 Legend BCG bolt face will be noticeably wider. However, visual inspection alone can be unreliable, especially if you are not familiar with both types of BCGs.
Another helpful tip is to check the manufacturer’s website or contact their customer service department. They should be able to provide information about the BCG’s compatibility with different calibers. When in doubt, it’s always best to err on the side of caution and consult with a qualified gunsmith.
The Role of the Magazine
While the BCG is a critical component, it’s also important to consider the magazine when switching between calibers. Standard 5.56 magazines are not designed to reliably feed .350 Legend cartridges. The .350 Legend has a larger case diameter and a different taper than the 5.56, which can cause feeding issues in a 5.56 magazine. Dedicated .350 Legend magazines are designed with the correct internal dimensions and feed lip geometry to ensure smooth and reliable feeding.
Using the correct magazine is just as important as using the correct BCG. Even if you have a 350 Legend BCG, using a 5.56 magazine can still lead to malfunctions.
Building a 350 Legend AR-15
Building a .350 Legend AR-15 requires careful attention to detail. In addition to the BCG and magazine, you will also need a barrel chambered in .350 Legend. The barrel is the most critical component, as it determines the caliber of the rifle. Ensure that the barrel is properly marked and that it is compatible with the other components you are using.
When assembling your .350 Legend AR-15, follow the manufacturer’s instructions carefully. Pay close attention to torque specifications and headspace measurements. If you are not comfortable performing the assembly yourself, it’s best to seek the assistance of a qualified gunsmith. [See also: AR-15 Build Guide]
Conclusion: Compatibility is Key
In conclusion, while a 350 Legend BCG may appear similar to a 5.56 BCG, they are not interchangeable. The key difference lies in the bolt face diameter, which is specifically designed to accommodate the different dimensions of the .350 Legend cartridge. Using the wrong BCG can lead to malfunctions, damage to the firearm, and potentially unsafe conditions. Always ensure that you are using the correct BCG, magazine, and barrel for the caliber you intend to fire. By understanding the nuances of these components, you can build a safe and reliable .350 Legend AR-15 that will provide years of enjoyment. Remember to always prioritize safety and consult with a qualified gunsmith if you have any questions or concerns. The 350 Legend BCG is designed specifically for the 350 Legend cartridge, and using it with any other cartridge is not recommended. Always verify the proper 350 Legend BCG is used for your firearm. Understanding these differences is key to safe and effective use of your AR-15 rifle. Always prioritize safety when handling firearms and ensure all components, including the 350 Legend BCG, are correctly installed and compatible with your chosen ammunition. Improper use of a 350 Legend BCG can lead to dangerous malfunctions. The correct 350 Legend BCG ensures proper cycling and safe operation. Remember to use a 350 Legend BCG with the correct magazine for optimal performance. Using the wrong 350 Legend BCG can be dangerous. Ensure you have the right 350 Legend BCG for your rifle. Always check your 350 Legend BCG for proper function. The 350 Legend BCG is a critical component for safe firing. Using the correct 350 Legend BCG will prevent malfunctions. Always inspect your 350 Legend BCG before use. A proper 350 Legend BCG is essential for reliable performance.
