300 Blackout Upper
Buy 300 Blackout Upper: Sig Sauer Upper Receiver Assembly Sig MCX Rattler 300 AAC Blackout 5.5″ with Tapered Lug M-LOK Handguard Black
$1,499.00 Add to cart

Buy 300 Blackout Upper: Sig Sauer Upper Receiver Assembly Sig MCX Rattler 300 AAC Blackout 5.5″ with Tapered Lug M-LOK Handguard Black


Product Information

Cartridge 300 AAC Blackout (7.62x35mm)
Finish Black
Material Aluminum
Barrel Length 5.5 Inches
Barrel Finish Black
Twist 1:5 Inches
Sights No
Upper Receiver Type A3 Flat-Top
Handguard M-LOK Handguard
Bolt Carrier Assembly Included Yes
Country of Origin United States of America
Compatible With
Sig Sauer MCX

Delivery Information

Shipping Weight 5.350 Pounds

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The Comprehensive Guide to 300 Blackout Uppers: Everything You Need to Know

Understanding the components of an AR-15 build can be a daunting task, particularly when it comes to the wide variety of uppers available in the market. One type of upper that has gained popularity among firearm enthusiasts is the 300 Blackout Upper. This guide will delve into everything you need to know about this versatile component and its variations.

Understanding the 300 Blackout Uppers

The 300 Blackout_Upper is a component of the AR-15 rifle, which forms the top half of the firearm. It comprises the upper receiver, the barrel, the gas system, and the bolt carrier group. One of the main reasons for the growing popularity of the 300 Blackout_Upper is its versatility. It offers the power of a 7.62×39 mm cartridge while fitting into a standard 5.56 mm AR-15 lower. This makes it a cost-effective solution for those looking to experiment with different calibers without investing in a new gun.

Unlike the standard 5.56 NATO upper, the 300 Blackout_Upper can fire subsonic or supersonic rounds, making it a great choice for suppressed shooting. Also, they are excellent for short barrel rifle (SBR) configurations as they don’t require a lengthy barrel to burn powder efficiently.

300 Blackout Upper

Why Choose a .300 Blackout Upper over Other Uppers?

The .300 Blackout_Upper comes with several advantages that set it apart from other uppers. First, it can fire larger and heavier rounds compared to the 5.56 NATO, resulting in higher bullet energy for the same amount of powder. This makes it a preferable choice for hunting or home defense.

Furthermore, the .300 Blackout Upper’s ability to seamlessly fit into a standard AR-15 lower receiver eliminates the need to buy a new firearm when switching calibers. This compatibility also extends to other components, including the bolt carrier group and the magazine, further saving on costs.

Finally, the .300 Blackout Upper’s capacity to fire both subsonic and supersonic rounds offers the flexibility to switch between stealth and power, depending on the situation. This dual capability broadens its usage spectrum, making it a worthy addition to any firearm enthusiast’s collection.

Different Types of 300 Blackout Uppers

The 300 Blackout Uppers come in various sizes and functionalities, each designed for specific uses. They are primarily categorized based on their barrel lengths. Some popular types include the 16 inch 300 Blackout Upper14.5 300 Blackout Upper8.5 300 Blackout Upper, and 5 inch 300 Blackout Upper.

The 16 inch 300 Blackout Upper provides a balance between accuracy and maneuverability, making it ideal for medium-range shooting. The 14.5 300 Blackout Upper and 8.5 300 Blackout Upper are perfect for close-quarters combat and suppressed shooting due to their compact size. The 5 inch 300 Blackout Upper, on the other hand, is best for pistol configurations due to its short barrel length.

300 Blackout Upper Piston vs Bolt Action Upper

When discussing the 300 Blackout_Upper, an exciting comparison that often comes up is between the Piston and Bolt Action Uppers.

The 300 Blackout Piston Upper operates using a piston system, where gas pressure from the fired cartridge is used to propel a piston that, in turn, pushes the bolt back to cycle the gun. This system keeps the receiver cooler, cleaner, and is considered more reliable, especially in adverse conditions.

In contrast, the 300 Blackout Bolt Action Upper uses a turn-bolt mechanism, where the shooter manually operates the bolt to eject spent cartridges and chamber new ones. While this system is slower, it also provides an unparalleled level of accuracy and consistency, making it highly favored by precision shooters.

Top Brands for 300 Blackout Uppers

Several reputable brands are known for their high-quality 300 Blackout Uppers. Some notable ones include Aero Precision, Diamondback, Geissele, Wilson Combat, and LMT. These brands offer a variety of features and configurations to suit various shooting needs. For instance, the Aero 300 Blackout Upper is praised for its durability and precision, while the Wilson Combat 300 Blackout Upper is known for its superior performance and craftsmanship.

How to Choose the Best 300 Blackout Upper

Choosing the right 300 Blackout_Upper depends on your specific needs and preferences. Here are a few factors to consider:

  • Barrel Length: Short barrels are great for close-quarters combat and suppressed shooting, while longer barrels are better for long-range accuracy.
  • Brand: Opt for well-known and reputable brands that offer quality products and good customer support.
  • Price: Your budget will significantly influence your choice. However, remember that a higher price tag often means better quality and performance.
  • Purpose: Identify your purpose for the upper. If you need it for hunting, you might need a different upper than if you want it for target shooting or home defense.
Best 300 Blackout Upper

300 Blackout Uppers and Lower Compatibility

One key advantage of the 300 Blackout_Upper is its compatibility with various lower receivers. Most notably, the 300 Blackout Uppers can work with a standard AR-15 lower receiver without requiring any special modifications. This means that you can switch between calibers simply by swapping the upper, making it a flexible and cost-effective option for those who enjoy experimenting with different ammo types.


To wrap up, let’s answer some of the most frequently asked questions about 300 Blackout Uppers:

Q1: Can you put a 300 blackout upper on a 556 lower?

Yes, you can. The 300 Blackout_Upper is designed to fit seamlessly onto a standard 5.56 AR-15 lower.

Q2: Will a 300 blackout_upper work on a 5.56 lower?

Yes, it will. This compatibility is one of the primary advantages of the 300 Blackout_Upper.

Q3: How can I build a 300 blackout_upper?

Building a 300 Blackout_Upper requires some gunsmithing skills. However, there are numerous guides and tutorials available online to guide you through the process.

Q4: Can I put a 300 blackout_upper on my current lower receiver?

Yes, provided your lower receiver is a standard AR-15 lower receiver.


The 300 Blackout_Upper is a versatile and efficient option for those looking to explore beyond the standard 5.56 NATO caliber. Its compatibility with AR-15 lowers, ability to fire larger rounds, and potential for suppressed shooting all contribute to its growing popularity among gun enthusiasts. Whether you’re a seasoned shooter or a budding gunsmith, the 300 Blackout Upper is a worthy addition to your collection.


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