Stern Defense Conversion Block - M&P and P320/P250 9mm and .40 S&W Magazines

Manufactured by Stern Defense
Manufactured by Stern Defense
1 Review

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NOTE: Limit 3 per household. Quantities exceeding 3 will not allow checkout.

We are fully staffed and processing orders. Standard orders are shipping in approximately 1 business day or less. FFL orders take approximately 5 business days if you can provide us an actively receiving FFL location.



The Stern Defense Magazine Conversion Block allows you to use 9mm or .40 S&W P320/P250 and M&P magazines in your favorite standard AR-15 lower receiver. This magazine adapter installs in seconds and features last round bolt hold open functionality – a welcome improvement when compared to other PCC builds. The Stern Defense MAG-ADMP9&40 adapter is constructed from 6061-T6 aluminum with a 4140 steel NiB coated feed ramp and are designed to be used with a Glock cut bolt. If you are looking to convert a standard AR to use 9mm or .40 caliber, this mag well adapter is a perfect start.

  • Designed for use with 9mm or .40 caliber barrels and Glock cut bolts
  • Constructed from 6061-T6 aluminum with type 3 hardcoat anodized finish
  • 4140 steel NiB coated feed ramp
  • Ergonomic magazine release
  • Last round bolt hold open
  • Works with all generations M&P, Sig P320, and P250 magazines
  • Works with any Mil-Spec lower receiver
  • Made in the U.S.A.

With pistol caliber AR-15s on the rise in popularity, Stern Defense is leading the way with innovative components to convert your standard AR lower to be compatible with pistol magazines from Glock, S&W, and even Beretta in a variety of calibers. Stern Defense is located in Missouri and dedicated to helping you build the ultimate pistol caliber carbine.
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BrandStern Defense
Fitment9mm or .40 P320, P250, M&P

WARNING: This Product can expose you to chemicals which is known to state of California to cause Cancer and Reproductive Harm. For more information, see

Ratings & Reviews

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This thing is awesome

by -

This thing is awesome. I purchased this along with a Stern Defense 9mm completed upper with an 8.5" barrel. I called Primary Arms and, on their recommendation, also purchased an H3 buffer. Cons: Initially, only one of my four Sig P320 mags would drop free but, with a little bit of sandpaper, I cleaned up the inside of the adapter (more like deburring) and now all four mags now work flawlessly. I ran about 150 rds through it today without a single hiccup.