One stock. Dozens of platforms.
A3 Industries × Haga Defense collaboration.
HDA3 is a modular stock and brace system from A3 Industries & Haga Defense, designed to integrate seamlessly across dozens of platforms.
The platform that doesn't exist.
The HDA3 is a modular stock and brace system engineered by A3 Industries & Haga Defense for use across a wide range of firearm platforms. Its interchangeable adapter system allows the same HDA3 assembly to be configured for different firearms without replacing the complete setup.
A hybrid construction combines aluminum and steel internal components with a lightweight polymer exterior, providing strength and rigidity without unnecessary weight. Platform-specific direct-fit adapters create a clean, integrated installation, while the 1913 Picatinny option provides broader compatibility.
Developed in collaboration with Haga Defense, the HDA3 brings together specialized materials knowledge and A3 Industries’ extensive platform and fitment experience. Every listed adapter is designed and tested on its intended firearm to ensure proper alignment, secure mounting, and dependable operation.
Explore the HDA3 collection:
Featured
HDA3 products:
HDA3 Brace to Stock Conversion
Universal fit
HDA3 Hybrid Polymer Brace - LWRC SMG45
Fits LWRC SMG45
HDA3 Hybrid Polymer Stock - Zenith ZF-56, ZF-300, ZF-39
Fits Zenith ZF-56 / ZF-300
HDA3 Hybrid Polymer Stock - Universal 1913
Fits FN SCAR, GForce Blade +2
HDA3 Hybrid Polymer Stock - Springfield Kuna
Fits Springfield Kuna
HDA3 Hybrid Polymer Stock - Sig MCX/Rattler
Fits Sig MPX / MCX
HDA3 Hybrid Polymer Stock - Robinson Arms XCR
Fits Robinson Arms XCR
HDA3 Hybrid Polymer Stock - PSA Jakl
Fits AR & Variants, PSA Jakl
HDA3 FAQ
What is the HDA3?
The HDA3 is a modular stock/brace system developed from a collaboration between Haga Defense and A3 Industries. The HDA3 was designed specifically to integrate seamlessly across dozens of firearm platforms without sacrificing strength or aesthetics to do so.
What firearms are HDA3 stocks and braces compatible with?
Virtually any platform that supports a 1913 Picatinny interface or has an available A3 direct-fit adapter.
When will the HDA3 be available?
The HDA3 was quietly released on March 24, 2025. The highly anticipated release was not announced in order to be fair to those that have been on the in-stock email notification lists the longest. The best way to find out when an HDA3 for your firearm will be available is to sign up to be notified by email when in stock. You can do this on the product page.
Are the HDA3s from Haga Defense and A3 Industries different?
The core HDA3 stock and brace components will be exactly the same no matter where you get them from but the firearm specific adapters may be different. For example a Bren 2 stock adapter from Haga Defense may have QD sling attachment machined into the aluminum where the A3 Industries variant will have a steel QD socket set into the aluminum adapter. Or the MP5 adapter from A3 Industries will be nylon while the adapter from Haga Defense will be aluminum. Be sure to check out both Haga Defense and A3 Industries to see all available options. Some options may be available on both websites and some only on one or the other. You can use the part number to identify which adapter a stock or brace has.
Example:
HDA3-MP5-HD-S-LF-BLK - Haga Defense
HDA3-MP5-A3-S-LF-BLK - A3 Industries
How do you fold the HDA3?
To fold the stock, grasp the stock placing your thumb over the top of the folding hinge. Press down with your thumb while lifting up on the stock to dislocate it. This will allow the hinge to fold. Hinges may be pretty stiff to operate when new. They will break in and become easier to operate over time with use.
Will the HDA3 be available in a right folding option?
The HDA3 will initially only be available with a left folding option. Right folding options are planned to be available at a later date as well as kits to convert left folding stocks to right and vice versa.
Will the HDA3 be available in more colors?
The initial release will be black only. FDE, ODG and Gray will follow shortly after. No other colors are currently planned.