Stern Defense

Stern Defense Mag-AD9


 Stern Defense has introduced a magazine block for standard AR-15 style rifles. 9mm converted AR’s are excellent for cheaper practice. Stern Defense was kind enough to send their AD9 magazine block. This product converts a regular AR-15 lower to accept Glock 9mm and 40 cal magazines. One will still need a complete 9mm AR upper, with a Glock style bolt, to work with the magazine block.

 The Stern Defense AD9 is probably one of the nicest magazine blocks around. It is beautifully machined and engineered. Made from 6061 aluminum, hard coat anodized, with some steel and plastic parts where needed, it should last a lifetime. The built in feed ramp is also NiB coated to help smooth out the transfer of the round from the magazine into the chamber. I also noticed this makes the feed ramp easier to clean. I ran various types and weights of 9mm through the AD9. All of them fed reliably, even my 124gr Gold dot hollow points.

 Installation of the magazine adapter is super easy. I used a standard forged mil-spec receiver. First, if new, just insert the adapter into the magwell, like you would any standard AR magazine. Push it until the standard magazine release clicks back out, just like the standard AR magazine. Now, on the bottom of the Stern Defense magazine block, are 3 screws. Take the supplied allen wrench and tighten up the gib screw, while pulling down on the adapter. The gib screw is the larger set screw toward the front of the adapter. What this does is force the gib (plastic piece at the front of the adapter) against the lower receiver’s magazine well. Then lightly tighten the other 2 smaller set screws until they touch the lower receiver. Now you are done with the hard part.

 This AD9 insert is great. I am using a Guntec USA BCG, which is cut for both the Glock style and Colt style, just for your info. Every magazine I have tried fed reliably. All the magazines drop free with a press of the magazine release. Now, the magazine release on the AD9 is a push forward type. Located if front of the trigger guard. All you have to do is push it forward with your trigger finger, and the magazines drop free. It took me a little bit to get the hang of this, but once I did, it works very nicely. If you try and hit the regular magazine release, it does absolutely nothing because of the mag block being wedged in with the gib. I used Glock, Magpul, ETS, and Amend2 magazines, all worked great, as mentioned above. Since the magazine release is only on the right side, left handed people will have to find a different way of releasing the magazines. I did find that if you push the magazine release with your left hand thumb, you can kind of strip the mag out, similar to an AK. I would love the magazine release to be ambidextrous and larger so that I don’t miss it when reloading quickly. Speaking of quick reloads, the magwell is also slightly beveled to help with the insertion of magazines.

Left hand using magazine release

 Some people may not see the purpose in a magazine block. I must admit, this thought has gone through my head before also. But, if you have a SBR, and want to run a short 9mm setup, a mag block allows someone to do this without having to pay another $200 tax stamp on a dedicated 9mm lower. Or if you are fortunate enough to have a full auto m16, you can convert it to 9mm with the AD9!

 I almost forgot to mention. The Stern Defense AD9 has last round bolt hold open. And it worked with all my magazines. It pushes up on the regular AR bolt release. So there is no need to learn any new aspects to your training, at least as far as the bolt release goes. The ejector is also part of the magazine adapter. Replacement ejectors are also available from Stern Defense.

 Stern Defense has made a great product. It is expensive, but worth it in my opinion. So if you think a magazine block might be for you, go check out Stern Defense.

Firearms Insider Reviews - 8 Key Points

Claim to Fame:

Magazine block to convert standard AR-15 lowers to 9mm Glock magazines

Target Market:

Those wanting a 9mm carbine on a standard AR-15 lower receiver

FNBs (Features & Benefits of this product):

  • Made in the U.S.A.
  • Constructed from 6061 T6 aircraft grade aluminum.
  • NiB coated feed ramp.
  • Hard coat anodized type 3.
  • Sturdy Construction.
  • Ergonomic mag release.
  • Works with all generations of Glock magazines.
  • Works with any mil spec ar15 lower receiver.
  • All gun components besides the Bolt and Barrel remain stock

What other aesthetic options or finishes are available?

Beretta 92, M&P, and M&P .45ACP

What others are saying?:

4 / 5 stars at Brownells

Building a 9mm AR Carbine on a budget can quickly become an expensive endeavor if you buy unreliable parts. The AR-15 9mm Conversion Adapter for Glock® Magazines by STERN DEFENSE Is a reliable way to use Glock magazines in a Mil-spec lower. I use it for USPSA PCC division and Steel Challenge matches to keep the feel of an M-4 and for training. I’ve personally tried other methods and this system is far superior. The feed ramp angle on 9mm is critical for proper function and reliability, with the vast array of projectile profiles. So far I’ve had luck with multiple types of 9mm projectiles I.E. Winchester 124gr FMJ, 145gr RN Bayou, and 147gr FP/HP Berry’s. The last round Bolt hold open is somewhat unnecessary for PCC, however, is great to feel the weight transfer of the bolt carrier group and buffer and have it lock on the last round. The only feature that I dislike is the magazine release is located at the bottom of the unit which is not a big deal if your state allows “standard capacity” magazines. However, I’d like index the same magazine release in the same configuration of an AR series firearm, which would be difficult without permanently modifying the magazine. Overall a great product the moment you open the package you can see that a lot of thought went into its development and manufacturer.

Link to other reviews:

Price point:

MSRP = $179.99

Retail = $179.99 at Brownells

I need it now! Availability:

Stern Defense or Brownells

Our Rating:


  • Easy Installation

  • Last round bolt hold-open

  • Beautifully made

  • Magazines drop free

  • Bevelled magwell


  • Price

  • Magazine Release is not in the standard location

Score: 8.50 GREAT



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