The Stern Defense Mag-AD9 9mm/.40 S&W Magazine Well Adapter (part no. 001SDMAGADMP9AND40/P32) installs in a standard mil-spec AR-15/M4/M16 lower’s magazine well to run 9mm/.40 S&W Smith & Wesson M&P and Sig P320/P250 pistol-caliber magazines, not a magazine itself. Stern Defense designed it to install in seconds with no gunsmithing, and it includes a last-round hold-open feature.

Key Specifications

• Converts a standard mil-spec AR-15/M4/M16 lower to run 9mm/.40 S&W pistol-caliber magazines.
• Accepts Smith & Wesson M&P and Sig P320/P250 magazines.
• Installs in the magazine well in seconds, no gunsmithing required.
• Includes a last-round hold-open feature.
• Manufactured by Stern Defense.

Frequently Asked Questions

What does this adapter do? It installs in a standard mil-spec AR-15/M4/M16 lower’s magazine well so the rifle can run 9mm/.40 S&W M&P and Sig P320/P250 pistol-caliber magazines instead of rifle magazines. It’s a conversion adapter, not a magazine.

Does it come with a magazine? No — it’s an adapter only; M&P and Sig P320/P250 magazines are sold separately.

Does it have last-round hold-open? Yes — the Mag-AD9 includes a last-round hold-open feature.

Buy the Stern Defense Mag-AD9 9mm/.40 S&W Magazine Well Adapter

Order the Stern Defense Mag-AD9 9mm/.40 S&W Magazine Well Adapter from our Lubbock, Texas gun shop for fast shipping. Browse more AR-15 lower parts at Schaefer Defense.