Pistol Caliber carbines have become extremely popular. The original 9mm AR-15 was made by Colt and used modified UZI magazines. With the popularity of pistol caliber ARs now there are lowers that can use Glock pistol magazines. However if you do not want to buy an entirely new lower then take a look at the Stern Defense MAG-AD9. It is a Glock magazines adapter that works in your mil-spec AR-15 lower.
With a Stern Defense mag adapter (MAG-AD9) you can use 9x19mm and .40s&w magazines in your AR-15 lower. You insert the mag adapter like you would a normal AR magazine. The AR mag catch acts as a shelf to hold the mag adapter. There is a pivoting delrin block that wedges into the mag well to help hold the mag adapter in place.
The bottom flange of the MAG-AD9 has a set of soft tipped set screws that pushes upward against the bottom of your AR magwell. This pushes the mag adapter downwards and since the normal AR mag catch is holding onto the mag adapter, these opposing forces keeps the mag adapter rigid.
Since the regular mag catch is now acting as a shelf for the mag adapter, make sure you do not push it to release your Glock magazine. The Stern MAG-AD9 has a separate magazine release which you can see below. You can push it with your index finger if you are right handed.
If you are left handed you can reach up with your support hand thumb and press the magazine release as you pull the magazine out of the mag well.
One feature that the MAG-AD9 has over other magazine adapter and even some dedicated 9mm AR lowers, is a functioning last round bolt hold. See the arched piece of metal? The follower pushes that up and there is a cam that helps lift the bolt catch on the last round. In front of the magazine you can see the feed ramp which is dirty in this photo but it is nickel boron coated steel.
And the upper?
Now that you have a Stern Defense mag adapter, you should also get a 9mm bolt. You can build a 9mm upper for not a lot if you look around. Blem AR uppers can be purchased for around $50 and 9mm AR barrels can be bought for around $100 if you look around for some good deals. Then all you need is a handguard. Choosing a 9mm bolt is somewhat important. You could use a Colt mag compatible 9mm bolt but you will need to send it in to Stern so they can under cut the bolt to make room for the last round bolt hold in their mag adapter. Or just buy their bolt. It is coated in nickel boron which makes cleanup super easy. Just wipe it down with a rag.
Stern Defense’s latest version of their 9mm bolt is now compatible with JP silent capture springs and LAW Tactical folding adapters. This bolt will even work with Fostech echo triggers. They come with a weight embedded inside the bolt. You just remove a set screw and pop out the weight if you want to use JP Silent capture springs or a LAW tactical folding adapter.
The Stern Defense MAG-AD9 retails for $179.99 and their newer bolt retails for $169.99. You could pretty much run any 9mm upper you want to but their bolt offers more features than any other 9mm bolt. The mag adapter is an inexpensive way to run a 9mm AR. Sure you could buy a dedicated 9mm lower but then you will have to finish building it with a lower parts kit, buffer, buffer spring, pistol grip, buffer tube and stock. You will easily spend over $180 to make a 9mm Glock magazine compatible lower. Aside from saving some money, the MAG-AD9 will work in full auto M16 lowers. So if you have a transferable select fire lower, you just throw the MAG-AD9 into it and slap on a 9mm upper and now you have a 9mm machine gun.