The Maxim Defense PDX SBR .300 Blackout in black is a subcompact short-barreled rifle built for close-quarters work (Maxim part no. MXM-47825). Maxim built the PDX in answer to the SOCOM PDW solicitation, and the .300 Blackout chambering is a natural partner for a 5.5-inch barrel. The SCW stock system takes the rifle down to 18.75 inches overall, and a HATEBRAKE muzzle booster handles recoil and flash. It runs both supersonic and subsonic .300 Blackout loads, which makes it an easy host for a suppressor on its 5/8×24 threads. For a rifle that fits in a backpack and still feeds from a 20-round magazine, the PDX is hard to beat.

Key Specifications

• The chambering is .300 Blackout, with a 20-round magazine capacity.
• Barrel length is 5.5 inches, which keeps the whole rifle subcompact.
• Overall length is 18.75 inches, the same collapsed or extended because of the SCW system.
• Weight is 5 pounds 11 ounces, as Maxim lists it for the PDX.
• The Maxim SCW stock system cuts the stock to 4 inches and includes an integrated bolt carrier group with interchangeable buffer weights.
• The muzzle carries the Maxim HATEBRAKE muzzle booster, which cuts recoil and flash and pushes gas and concussion downrange.
• Muzzle thread pitch is 5/8×24, the pattern to match for muzzle devices and suppressors.
• The trigger is the ALG trigger Maxim fits to the PDX.
• The finish is Type III hard coat anodize in black, a durable coating for the aluminum parts.
• Construction uses 6Al-4V titanium, 17-4 stainless steel and 7075 and 6061 aluminum, with an M-slot compatible handguard and an HK height rail for a more rigid upper.

Frequently Asked Questions

Do I need ATF approval to buy this? No. As of October 9, 2026, ATF no longer requires Form 4 approval, registration or a tax stamp for short-barreled rifles. It transfers on a Form 4473 with a background check through a Class 3 (SOT) dealer. State and local laws still apply. Taking an SBR across state lines still requires an approved ATF Form 5320.20.

Which muzzle thread does the .300 Blackout PDX use? Maxim lists 5/8×24 for the .300 BLK and 7.62x39mm PDX, and the rifle ships with the HATEBRAKE muzzle booster installed.

What stock does the PDX SBR use? It uses the Maxim SCW stock system, which shortens the stock to 4 inches and carries an integrated bolt carrier group with interchangeable buffer weights.

Buy the Maxim Defense PDX SBR .300 Blackout, Black

As of October 9, 2026, this short-barreled rifle transfers on a Form 4473 with a background check at your Class 3 (SOT) dealer, with no Form 4 or tax stamp; state and local laws still apply. Order through Maxim Defense‘s short barrel rifles lineup and our Lubbock, Texas team will handle the transfer, and it ships fast to your Class 3 dealer.