The FN 5.7x28mm cartridge has carved a niche for itself, known for its unique ballistic characteristics and suitability for specific applications. Its adoption in AR-15 uppers has sparked considerable interest among shooters and enthusiasts seeking a distinct shooting experience. This detailed exploration delves into the specifics of FN 5.7 AR-15 uppers, examining their performance, practical considerations, and overall value proposition.
Understanding the FN 5.7x28mm Cartridge
Before diving into the upper receivers, it's crucial to understand the ammunition itself. The 5.7x28mm is a relatively small, high-velocity round designed for penetration and low recoil. Its characteristics make it an interesting choice for certain scenarios, but it’s important to understand its limitations compared to more traditional AR-15 calibers like 5.56 NATO or .223 Remington.
Key Characteristics:
- High Velocity: The 5.7x28mm boasts significantly higher velocity than many other pistol calibers, leading to flatter trajectories and increased effective range.
- Penetration: Designed to penetrate barriers such as soft body armor, the 5.7x28mm offers superior penetration compared to calibers like 9mm.
- Low Recoil: Its smaller size and lighter weight contribute to noticeably less felt recoil.
- Limited Stopping Power: While its penetration is high, the 5.7x28mm's relatively low mass results in potentially less stopping power compared to larger calibers.
FN 5.7 AR-15 Upper Receivers: Design and Functionality
Converting an AR-15 platform to fire the 5.7x28mm requires a specialized upper receiver. These uppers are specifically engineered to accommodate the smaller cartridge and its unique dimensions. Key design features often include:
- Bolt: A modified bolt carrier group (BCG) is essential, designed for the specific dimensions of the 5.7x28mm cartridge.
- Barrel: The barrel is chambered for the 5.7x28mm and typically features a faster twist rate to stabilize the lighter projectiles.
- Magazine Well: A dedicated magazine well is necessary for proper magazine compatibility. Standard AR-15 magazines will not function.
Performance and Practical Applications
The performance of an FN 5.7 AR-15 upper receiver is largely determined by the specific components used (manufacturer, barrel length, etc.). However, some general observations can be made:
- Accuracy: While accuracy can be good, it's often affected by the lighter bullet weight and the sensitivity to wind.
- Range: The high velocity translates to a relatively flat trajectory, allowing for accurate shots at extended ranges compared to other pistol calibers.
- Recoil Management: The low recoil is a significant advantage, particularly for newer shooters.
Practical Applications:
The 5.7x28mm's unique characteristics make it a niche option. While not suitable for all applications, it can be advantageous in specific situations:
- Home Defense (debatable): Some argue its penetration capabilities could be a concern in densely populated areas.
- Personal Protection: Its combination of penetration and low recoil might be appealing for personal protection.
- Training: The low recoil makes it ideal for training new shooters or improving marksmanship skills.
Considerations Before Purchasing
Before investing in an FN 5.7 AR-15 upper, carefully consider the following:
- Ammunition Cost: 5.7x28mm ammunition is generally more expensive than more common calibers.
- Ammunition Availability: While availability has improved, it may still be less readily available than other calibers.
- Specific Use Case: Ensure the 5.7x28mm's unique characteristics align with your intended use.
Conclusion: A Specialized Tool for a Specific Job
FN 5.7 AR-15 uppers offer a unique shooting experience. Their combination of high velocity, low recoil, and penetration capabilities caters to a specific niche. However, potential buyers should thoroughly weigh the cost, availability of ammunition, and the cartridge's limitations before making a purchase. This in-depth understanding ensures the informed selection of a tool that aligns perfectly with individual needs and expectations.
