MAG-AD MP9/40 + P320 – Magazine Adapter for M&P & Sig Sauer Magazines

Convert. Adapt. Perform.

THIS PRODUCT MUST BE USED WITH A 5.4 OZ BUFFER OR HEAVIER WHEN USING A CARBINE SPRING.
? [Click here to get the recommended buffer]

⚠️ NOTE: The new 30-round Sig magazine is not compatible with this adapter.

Turn your mil-spec AR-15, M4, or M16 lower into a 9mm or .40 S&W powerhouse using your M&P, P320, or P250 magazines. The MAG-AD MP9/40 + P320 installs in seconds with no permanent modifications—perfect for both law enforcement professionals and dedicated civilian shooters.

Featuring true last-round hold open, this is one of the most trusted magazine conversion systems available today.

Why Choose the MAG-AD MP9/40 + P320?

Fast drop-in installation
Fully compatible with M&P, Sig Sauer P320, and P250 magazines
Works with mil-spec AR-15 lowers
Lightweight aircraft-grade aluminum body
Built-in ergonomic mag release
Made entirely in the USA

Technical Specs

CNC-machined from 6061-T6 aluminum
4140 NiB-coated feed ramp
Hard coat anodized (Type III) for maximum wear resistance
Works with Glock-cut bolts
Requires a caliber-specific barrel in 9mm or .40 S&W
Keeps all other internal components stock (except barrel/bolt)

Need Additional Components?

Already have a Colt-style bolt? [Click here]
Need a new bolt? [Click here]
Need a new barrel? [Click here]

Important Compatibility Note

Before ordering, be sure your setup is compatible.
[Check compatibility here]

5 Reviews Hide Reviews Show Reviews

5
High Quality Manufacturing

Posted by Ernesto on Feb 14th 2022

Awesome! Works with P320 Legion mags and ProMag P320 mags.
5
P320 9mm adapter

Posted by Barry on Jul 9th 2021

LOVE IT! Quality, installation, function, all great. Tested endomags first...ugh.
5
Quality product that functions

Posted by Brian Harris on Jan 23rd 2020

im super pleased with how well my sbr runs with this! the only thing i could ask for would be the logo cut in during the milling process and then anodized so i dont have the "nascar" branding. but if thats all im complaining about, this earned the 5 stars. Also the Glock cut for basically free shows this company know how to take care of a customer.
5
MAG-ADMP9&40

Posted by Brent Janzen on Nov 26th 2019

The MAG-ADMP9&40 performs very well. The magwell adapter installs in seconds, and is very secure in my M&P15T lower. Only a few misfeeds, but more likely caused by the Promag M&P 32rd clips not being broken-in. Thanks Stern Defense.
5
Awesomeness defined!

Posted by Ranger Doc on Oct 28th 2019

Purchased this as part of the basic build kit. Using in an Aero Precision lower. The device works perfectly and the design is great and simple to use. I did have to do some minor fitting on my Aero lower. When installed, the magazine release would not function. The part that extends upward to engage the magazine's notch was rubbing on the inside of the mag-well of the lower. When examining the lower I could see that the broach cut for the mag-well left a small layer of extra material at the front side of the mag-well. I simply filed this down so that the entire side of the inside of the mag-well was level and smooth. This fixed the issue completely. NOT a fault of this product at all, but likely a common issue with tight fitting mag-wells.