The Stern Defense Mag-AD9 is an adapter designed to allow standard mil-spec AR-15 lowers to accept S&W M&P and SIG P320/P250 pistol magazines in 9mm and .40 S&W. Constructed from aircraft-grade aluminum and finished with a Type III hard coat anodize, the adapter installs in minutes and retains standard AR-15 lower ergonomics. The design includes a 4140 NiB-coated feed ramp and supports the adapter’s last-round hold-open functionality when used with compatible magazines and a Glock-cut bolt. Intended for builders and shooters converting an AR lower for pistol-caliber magazines and low-recoil rifle configurations.
Key Specifications
- Constructed from 6061-T6 aircraft-grade aluminum.
- Finished with Type III hard coat anodize.
- Includes a 4140 NiB-coated feed ramp.
- Accepts S&W M&P and SIG P320/P250 magazines for 9mm and .40 S&W.
- Designed to fit mil-spec AR-15 lower receivers.
- Requires a Glock-cut bolt.
- Recommends a 5.4 ounce buffer or heavier when using a carbine spring.
- Overall dimensions listed as 3.45 x 4.40 x 8.65 inches.
- Manufactured in the United States.
Whether you are building a pistol-caliber carbine for economical range time or converting an existing AR platform to run S&W M&P or SIG P320/P250 magazines, the Mag-AD9 provides a robust, aircraft-grade solution. The adapter’s durable materials, proven feed ramp finish, and straightforward installation make it a practical component for builders and shooters seeking reliable magazine compatibility in 9mm and .40 S&W configurations.
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