Maxim Defense Industries PDX, Complete Upper, 300 Blackout, 5.5″ Barrel

Product Description

The Maxim Defense Industries PDX complete upper in 300 Blackout features a 5.5″ barrel and is designed for compact weapon systems where reduced overall length is critical. This upper assembly is built for shooters who need maximum maneuverability without sacrificing terminal ballistics.

The PDX platform from Maxim Defense represents a purpose-built approach to ultra-compact rifle configurations. The 300 Blackout chambering delivers effective performance from short barrels, particularly when paired with subsonic ammunition and a suppressor.

This complete upper is ready to mate with a mil-spec lower receiver. It suits home defense, vehicle applications, and any scenario where space is limited but firepower cannot be compromised.

Key Facts

• Manufacturer: Maxim Defense Industries
• Model: PDX Complete Upper
• Caliber: .300 Blackout
• Barrel Length: 5.5″
• SKU: MXM-47826

Why the PDX Upper Configuration Matters

A complete upper arrives as a single assembly, meaning the barrel, bolt carrier group, charging handle, and handguard are already fitted and headspaced. This saves time and eliminates the need for specialized tools or torque specs. You install it onto a compatible AR-15 lower receiver using two takedown pins, just as you would field-strip the rifle.

The PDX upper design prioritizes compactness. Shooters often choose this configuration for builds where traditional carbine-length uppers are too long for the intended role. It pairs well with pistol braces or short-barreled rifle lower receivers, depending on your NFA compliance status.

300 Blackout in a 5.5″ Barrel

The 300 Blackout cartridge was engineered to perform from short barrels. Unlike 5.56 NATO, which loses significant velocity and reliability below ten inches, 300 Blackout maintains powder burn efficiency and cycling reliability even in barrels shorter than six inches. This makes the caliber ideal for ultra-compact platforms like the PDX upper.

Subsonic 300 Blackout loads perform especially well in this configuration. When suppressed, the combination offers reduced sound signature and minimal muzzle blast, making it a popular choice for close-quarters applications. Supersonic loads remain viable for situations where barrier penetration or energy at distance is required.

What to Confirm Before You Order

If you need to verify handguard length, gas system type, muzzle threading, or rail attachment standard, call us at 817-393-4000. Those details affect accessory fit and suppressor attachment, so it’s worth confirming before you buy.

Check your lower receiver for compatibility. This upper fits standard mil-spec AR-15 lowers. If you’re building a pistol, ensure your lower is configured accordingly. If you’re registering this as a short-barreled rifle, an approved ATF Form 1 is required before you assemble the complete firearm.

Buying from Western Sport in Roanoke, TX

Western Sport is a licensed FFL/SOT dealer serving the North Texas and DFW area since 2007. Our gunsmith, Lance Rankin, handles transfers, special orders, and custom builds on site. If you have questions about fitment, NFA compliance, or pairing this upper with a specific lower, call 817-393-4000.

Frequently Asked Questions

Q: What is the Maxim Defense PDX upper?

A: The Maxim Defense PDX upper is a complete upper receiver assembly chambered in 300 Blackout with a 5.5″ barrel. It installs onto any mil-spec AR-15 lower receiver and is designed for compact weapon configurations.

Q: Does the PDX upper work with standard AR-15 lower receivers?

A: Yes, the PDX upper mates with any mil-spec AR-15 lower receiver using the standard takedown pin system. No modifications or adapters are required for installation.

Q: Can I use this upper on a pistol lower or does it require an SBR stamp?

A: You can install this upper on an AR pistol lower that is configured with a brace rather than a stock. If you want to attach it to a lower with a rifle stock, you must first receive an approved ATF Form 1 to register the complete firearm as a short-barreled rifle.

Q: Why choose 300 Blackout in a 5.5″ barrel instead of 5.56 NATO?

A: The 300 Blackout cartridge was designed to function reliably in barrels shorter than seven inches, maintaining complete powder burn and proper gas cycling. The 5.56 NATO round loses substantial velocity and may experience reliability issues in barrels this short, making 300 Blackout the better choice for ultra-compact platforms.

Q: What handguard or rail system should I expect on the PDX upper?

A: Call 817-393-4000 to confirm the handguard type and attachment standard before you order, especially if you need to mount specific accessories or verify clearance for a suppressor.

Q: Can Western Sport handle the transfer if I’m in the DFW area?

A: Yes, Western Sport is a licensed FFL dealer in Roanoke, Texas, serving the North Texas and DFW area. We process transfers for complete AR uppers and other firearms. Call 817-393-4000 to arrange your transfer or ask about the process.

Additional information