Stern Defense SIG P320/S&W M&P9 Mag Adapter

    Stern Defense magwell adapters are a great way to caliber convert a mil-spec AR-15 lower to shoot a pistol caliber. They started with a Glock magazine adapter. Check out my review of their MAG-AD9. They have also made adapters to use Beretta 92 magazines and even M&P 45 magazines. However, their latest design uses SIG P320 magazines which also doubles as an M&P9 mag adapter.

    One Adapter: Two Magazine Types

    Their latest pistol magazine adapter works with SIG P320 magazines as well as S&W M&P magazines. So if you have either one of those handguns, you can get this adapter to use those handgun magazines to feed a pistol caliber AR-15.

    The 320 adapter has a slightly tight fit for the P320 magazines. They do not drop free.

    Sig P320 magazine above and S&W M&P magazines below.

    Just like their MAG-AD9 adapter, the Stern Defense P320 adapter has a similar mag catch/release and functioning last round bolt hold mechanism.

    When I checked my friend’s SIG P320 I tried swapping magazines. SIG P320 magazines would not fit in my M&P9 but my M&P magazines could fit in the P320. I don’t know if the M&P mags will feed a SIG P320.

    The new Stern Defense P320 adapter MAG-ADMP9&40/320 retails for $186.99. You can use it with either SIG P320 magazines or Smith and Wesson M&P9 magazines which makes it more versatile than a stand-alone dedicated lower for either magazine. This gives you more flexibility with magazine options. You can rock SIG P320 mags for your SIG P320 and then use them in your AR PCC. And for added capacity you can use those 30 rd M&P magazines by Promag or if your buddy has an S&W M&P and lends you some of his mags you are good to go.

    Technical Information:

    ⦁    Made in the U.S.A.

    ⦁    Constructed from 6061 T6 aircraft grade aluminum.

    ⦁    4140 NiB coated feed ramp.

    ⦁    Hard coat anodized type 3.

    ⦁    Sturdy Construction.

    ⦁    Ergonomic mag release.

    ⦁    Works with all generations of M&P magazines.

    ⦁    Works with P320 and P250 magazines

    ⦁    Works with any mil spec ar15 lower receiver.

    ⦁     All gun components besides the Bolt and Barrel remain stock

    For more information on the Stern Defense P320 adapter, go check out Stern Defense.



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    Nicholas C

    Steadicam Gun Operator
    Night Vision & Thermal Aficionado
    Flashlight/Laser Enthusiast
    USPSA competitor

    Any questions please email him at [email protected]


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