ProMag Adapter: Convert Your Standard AR-15 Lower to 9mm

I love PCCs, and if the industry knows its audience, it seems like I’m not the only one. There used to be a time where PCCs weren’t rare, but they weren’t common. You could find one, but not every company on the market was producing them. These days everyone sells one. The AR9 market is a dominant option, and the modularity of the AR-15 allows for several different types, sizes, configurations, and calibers. If you want a PCC on a tight budget, the AR is the route to take. If you want to maximize affordability, then the ProMag Quick Change Adapter is for you.

promag block for conversions
The block installs with ease.

The ProMag Quick Change Adapter drops into your standard MIL-SPEC AR-15 lower receiver’s magwell. This adapter converts your magwell to the widely available Colt SMG magazines. Colt SMG mags aren’t as popular as Glock mags these days, but they are affordable, widely available, and are true SMG magazines. They are robust, feature a last-round bolt hold open, and are a true double stack, double feed magazine.

The ProMag Quick Change can save some cash by using the AR lower you already have. I’d swap the buffer for a heavy model, but that’s all you need to do. If you don’t have an AR-15 already, the standard Multi-Cal MIL-SPEC forged lowers are the cheapest option. Dedicated PCC lowers always have a premium attached due to the nonstandard design.

The Installation Process

Installation is super simple. ProMag thinks it’s simple enough you don’t need instructions, and they don’t even post a how-to on their website. Luckily the internet ensures it’s easy to find videos showing the installation.

You don’t need any tools and do not have to alter your lower receiver in any way. The Quick Change adapter comes in two pieces. The rear piece features the hook-shaped ejector, and the front piece has your feed ramps.

Install the rear piece first. You have to make sure the piece is flush with the rear of the magwell. There is a small silver piece that needs to align with the bolt hold open device. Make sure you press the magazine release button as you slide the rear portion upward.

Installed promag conversion kit
The LRBHO engages easily.

Once the rear portion is in, just slide in the front portion, and bam, you’re done. Test for function with a magazine. I used the steel ASC mags, and they fit perfectly. Your controls are unchanged. The magazine release works, as does the bolt release. The ProMag Quick Change Adapter doesn’t require much to get you spun up.

You’ll need to get a 9mm upper receiver with a Colt SMG bolt. There is a difference between Glock and Colt BCGs, so make sure you get the right one. This has to be a basic 9mm receiver, likely a straight blowback model. Plenty of companies make them, including budget-friendly sources like PSA.

At the Range

With the ProMag Quick Change Adapter in hand, I hit the ground running. I had two COlt ASC magazines and one of ProMag’s own polymer Colt SMG mags. With a rifle, optic, and bucketful of mixed ammo, I hit the range. First things first, how does it handle in the general reliability department?

Over several hundred rounds, the adapter gave zero issues. I only had issues with the polymer Colt SMG mag. I tossed it to the side and focused on just the metal mags. There is some odd wobble with the mags and the adapter. They didn’t sit still, and you could move them ever so slightly backward and forward. I shot with the mags in both positions, and there weren’t any issues either way.

Colt-style AR magazine in AR rifle
The magazine looks odd in a MIL-SPEC lower receiver.

I wondered if the feed ramps would handle JHPs, and surprisingly, they did. Bonded JHPs from Sig worked without complaint, as did normal brass-cased FMJs, and that ultra-dry Winchester Forged junk worked fine with one issue with ejection. That bugger stuck to the bolt and required a tool to remove. Crappy ammo tends to perform like crap.

The block itself holds the magazines tightly. This means when you hit the mag release, they don’t fall out freely. They require a tug to release to reload. It’s surprising because the magazines are all metal and fairly heavy. Tossing another mag isn’t hard, but the magwell looks 5.56 sized, and it’s easy to slam the mag in the wrong place when moving quickly. It will take a little practice and lots of reps to get right. You also got to apply a little force to get those magazines in place.

Blasting Away

I tested the gun with the magazine in several different positions. I rested the mag on the ground as if it was a monopod and didn’t run into any malfunctions. The ProMag Quick Change Adapter does a good job of limiting the upward movement of the magazine. Second, I pressed and pulled the magazine against a barrier, and again, no issues with reliability. The adapter and ASC mags work very well together.

magazine in gun
32 rounds of 9mm are on tap with the Colt SMG mag and ProMag conversion block.

The idea is that this is a quick change adapter, so I wanted to see how fast and easy it was to pop out. The process is the reverse of the installation. Push downward on the feed ramp, and it pops out. Press downward on the magazine well, and it pops out. The process isn’t complicated. You need to hit the magazine release and push the adapter downward. You need to use a good bit of force to get the thing to slide out.

It doesn’t drop out easily, and it certainly will never accidentally fall out or move. Oh, and since it’s a blowback-operated gun, the adapter will get filthy in short order, so be ready to wash your hands.

Lrbho design of promag quick change adapter
The Colt mags trigger the guns LRBHO.

Finding Purpose

Where exactly does the ProMag Quick Change Adapter fit in? Well, it could be used for home defense, but a standard 5.56 rifle will have less recoil and more power. It’s not going to be great for competition due to the somewhat slow reloads. What it does fit is in the fun category. PCCs are fun, cheap to shoot, allowed at most outdoor ranges, and easy to suppress.

While the ProMag Quick Change Adapter isn’t as good as a dedicated PCC and PCC magazine solution, it’s pretty darn close. It’s an affordable way to get into the 9mm rifle realm and makes use of that famed AR modularity.

Travis Pike is a former Marine Machine Gunner and a lifelong firearms enthusiast. Now that his days of working a 240B like Charlie Parker on the sax are over he's a regular guy who likes to shoot, write, and find ways to combine the two. He holds an NRA certification as a Basic Pistol Instructor and is probably most likely the world's Okayest firearm instructor. He is a simplicisist when it comes to talking about himself in the 3rd person and a self-professed tactical hipster. Hit him up on Instagram, @travis.l.pike, with story ideas.

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