Introducing the Maelstrom Pro

The MAC-11 platform has remained popular for decades because of its simplicity, reliability, and aftermarket support. Whether built on an original lower, a modern commercial variant, or a home-built firearm, the platform continues to attract builders looking for a compact and customizable firearm.

The Maelstrom Pro was developed to bring delayed-blowback operation to the MAC platform while maintaining compatibility with standard MAC-11 components.

Unlike traditional sheet-metal uppers, the Maelstrom Pro combines a fully machined monolithic receiver, a non-reciprocating folding charging handle, and a detent-delayed operating system into a single package. The result is a softer recoil impulse, reduced or eliminated bolt bounce*, modern optics compatibility, significantly less gas to the face (especially when suppressed), and improved ergonomics while retaining the familiar MAC footprint.

Maelstrom PRO 8" Upper on a Free State Gun Co. lower with an A3 Industries 6.5" Modular Side Folding Stock

Compatibility

No proprietary bolt is required. The Maelstrom Pro is designed to work with standard full-size MAC-11 pattern bolts and MAC-pattern lowers, allowing builders to continue using many of the components already available within the MAC ecosystem. Maelstrom uppers have been tested on Velocity V-MAC, MPA Defender (aluminum and sheet metal), Free State Gun Co. SAS-9/M8, and other lowers. Because bolt manufacturers use different spring rates, firing pin designs, and manufacturing processes, we recommend reviewing our MAC-11 Bolt Compatibility & Tuning Guide before selecting a bolt assembly.

Maelstrom PRO 8" Upper on a Free State Gun Co. lower with an A3 Industries 6.5" Modular Side Folding Stock

Modernized Design

The Maelstrom Pro was designed from the ground up as a modern MAC upper receiver.

A continuous 23-position Picatinny rail provides ample space for optics and accessories, while the folding non-reciprocating charging handle eliminates the drawbacks associated with reciprocating charging systems.

The upper receiver and charging handle are machined from billet 6061 aluminum and finished in Cerakote Gen II Graphite Black (HIR-146). The trunnion and charging handle carrier are machined from 17-4PH stainless steel and heat-treated to H900 condition for long-term durability.

Maelstrom PRO 5.5" Upper on a Velocity V-Mac Lower with a Sig Sauer MCX/MPX Minimalist Locking Folding Stock

Future Plans

Initial release models will be chambered in 9mm. Additional caliber offerings are planned for future release, with 5.7x28mm being next on the list.

Features & Specifications

Operating System: Detent-delayed blowback

Receiver Material: Billet 6061 aluminum

Handguard Material: 8" models include a 6063 aluminum free-float M-LOK handguard with top Picatinny rail

Finish: Cerakote Gen II Graphite Black (HIR-146)

Stainless Steel Components: 17-4PH stainless steel trunnion and charging handle carrier, heat-treated to H900 condition

Barrel Options: 5.5" or 8"

Caliber: 9mm

Twist Rate: 1:10

Muzzle Threads: 1/2x28

Charging System: Folding non-reciprocating charging handle

Optics Mounting: Continuous, full-length monolithic 23-position Picatinny rail

Magazine Compatibility: Standard and dual-feed

Also Available: The Maelstrom

For builders who prefer traditional straight-blowback operation, we also offer the standard Maelstrom upper.

The standard Maelstrom shares the same monolithic receiver design, continuous top rail, and folding charging handle while retaining conventional straight-blowback operation.

In Closing

The MAC platform has always evolved through its builders, and more recently through the rapid innovation coming from the 3D2A community. We're proud to contribute to the next chapter and can't wait to see what the community creates!

*During testing with bolts from multiple manufacturers, we observed zero bolt bounce across all bolts evaluated. Results may vary depending on the specific bolt, ammunition, and configuration used.