Best 9MM AR Upper Conversion

The AR rifles, specifically the AR-15, are the most popular guns sold in America. But the standard 5.56mm NATO may not be what you’re looking for. A lot of people are opting to convert their AR to fit the common 9mm caliber.

To do that, you can either take it to a gunsmith or you buy an upper Conversion kit and do it yourself. There are a lot out there, so we took a look and found the 5 best 9mm AR upper conversion kits around. Read on for more information and our reviews below.

Product Our Rating Scenario
COLT AR-15 9MM DEDICATED CONVERT 4.3/5 Budget Friendly
ROCK RIVER AR-15 9MM CONVERSION 4.2/5 Alternative #1
BROWNELLS AR 9MM CONVERSION 4.0/5 Alternative #2

Review of the Best AR Upper Conversions

best 9mm ar upper conversion

In this next part, we review our picks for the best AR upper conversions. Keep the features from above in mind as you read on and find the best product for your needs.

Brownells AR-15/M16 9mm Drop-in Conversion Blocks

Though Brownells drop-in conversion block may be the highest price on the list, you may find it worth it. The kit has many features that might just suit your needs.

Brownells designed this conversion block to fit with any Colt style 9mm receiver for the AR and also to work with the AR-15/M16 lower receiver. The drop-in design makes it simple to switch in and out with little effort on your part. All it takes is some know-how.

The block is machined from aluminum for a lightweight and durable material. It also works with all variations of 9mm ammo including hollow point and frangible ball.

Included with the conversion kit is a roller retention device that stops the block was releasing from the receiver accidentally. Once the part’s in, it’s in until you take it out.

Brownells augments the aluminum with steel in key places like the ejector, feed ramp, and bolt hold open. Putting the tougher material here increases the durability and life of the part.

No modification is required of existing receiver parts. Brownells made this in a bottom-loading and top-loading orientation.

Here’s what actual users had to say:

Positives Recap for This Product

  • Easy to install
  • Great hybrid material
  • Machined quality ensures good fit
  • Fits with standard parts
  • Drop-in style for easy switching

Negatives Recap for This Product

  • Requires an additional bolt catch to use

Colt AR-15/M16 9mm Dedicated Conversion Block

This dedicated conversion block by Colt is the most affordable on the list. If you’re only looking for help converting your lower receiver to take 9mm, then this is the product for you.

As with other high-quality conversion kits, Colt makes this from an aluminum And steel Hardware. The combination of the two gets the best of both worlds: light weight from the aluminum and durability from the steel.

The conversion block accepts Colt style magazines and works with Colt upper receivers. It can also work with Metalform and Brownells if needed.

When customers used the part, they had this to say:

Positives Recap for This Product

  • Affordable price
  • Great hybrid material with a long life
  • Fits with different brands for 9mm parts

Negatives Recap for This Product

  • Needs modification of the existing receivers to work correctly

Rock River Arms AR-15/M16 9mm Drop Conversion Block

This conversion block by River Rock Arms is in the middle of the road as far as price, but it still may be what you’re looking for. As a drop-in design it’s meant to be easy to use, and it is. To install this part, all you have to do is insert the block into the magazine well and the standard mag catch locks it in.

Rock River Arms makes this out of steel and aluminum. The steel received a matte black oxide finish to prevent rust. The aluminum adds to the lightness of the part and received a matte black hardcoat anodized finish.

This part fits AR-15/M4 collapsible models as well, and it has a .154” diameter for receiver pin holes. The Rock River Arms block works with Colt magazines and modified UZI magazines.

Users reported the following about the product experience:

Positives Recap for This Product

  • Great hybrid material with good finishes add to the long life of the part
  • Easy to switch in and out
  • Fitting with collapsible models is a nice plus

Negatives Recap for This Product

  • May not work as well with UZI magazines

Hahn Precision AR-15/M16 9mm Drop-in Conversion Blocks

Hahn Precision’s conversion block is cut from the same cloth as the Brownells conversion block but at a more middle price. The part is made from aluminum and machined to precise measurements. This makes it lighter and easier to use.

The ejector, feed ramp, and bolt hold open are made from steel for long life. These are the parts that receive the most pressure during use, so making it out of steel there is a good choice.

Hahn Precision’s part works with Colt and modified UZI magazines. It comes in a bottom-loader and upper-loader orientation. The upper model requires the removal of the bolt release, so it can’t be considered a true drop-in block.

Customer using the product had this to add:

Positives Recap for This Product

  • Easy to install
  • Great hybrid material
  • Machined quality ensures good fit
  • Smooth function with different types of 9mm ammo
  • Drop-in style for easy switching

Negatives Recap for This Product

  • Top-loading needs to remove the bolt catch

Stern Defense AR-15 9mm Conversion Adapter

The Stern Defense Conversion Adapter is a medium-priced kit that tries to make your AR feel just like it normally does but with 9mm ammo. After installing, you won’t notice much of a difference in the mechanics of the weapon, but you’ll still get what you want out of the smaller ammo.

Stern Defense makes the adapter out of aircraft grade aluminum for light weight and reliability. The ergonomic design makes it easy to handle as you install it within seconds according to the company. They really tried to make this adapter useful in the field.

Once it’s installed in any mil-spec AR-15 lower receiver, it goes into use without any problems. It even comes with a bolt hold open when you’ve fired your last round.

They offer two versions of the adapter to specifically fit Glock magazines and Smith and Wesson M&P mags. These are unlike the others on our list, so if you prefer using these kinds, this may be the conversion for you.

People using this conversion adapter describe the experience like this:

Positives Recap for This Product

  • Aluminum is light but still sturdy
  • Fit with Glock and Smith and Wesson is unique
  • Easy to install in seconds
  • Affordable pricing

Negatives Recap for This Product

  • No consistent complaints were found

Why convert your AR to the 9mm?

You might wonder, “Why change the ammo at all? Isn’t the 5.56mm NATO the standard for AR rifles?”

Yes, you’re right, but there are some circumstances that may guide you towards converting to the 9mm. Check out some of these reasons below.

Lower cost – 9mm rounds cost much less than the standard rifle ammo. While you’re not going to use the ammo like you would out of a pistol, you can still enjoy the savings if you shoot a lot at the firing range.

Less noise and recoil – The smaller caliber has less of a punch to it. When your fire, the noise is going to be quite a bit less. With smaller ammo, the recoil is also less which makes it more comfortable to shoot.

Improve the range of the 9mm – If you just like shooting the 9mm (and why not? It’s an effective caliber), firing it through an AR rifle gives it more range and more speed.

Make your ammo more versatile – If you convert the AR rifles and your other guns all to take the 9mm, you’re making each round you buy or make more versatile. You can pick any gun and not have to worry about if you got the right ammo. This would be useful in emergency situations where you didn’t have time to worry about what you were grabbing.

It’s fun to play and customize – The AR has a reputation as the LEGO of the gun world. This doesn’t mean that it’s a toy by any means, but it refers to how customizable the rifle is. Using the 9mm upper conversions can make your gun exactly how you want it to be, and it’s a great conversation piece at the shooting club.

Features of Conversion Kits

Not all conversion kits are made the same. There are some things you need to watch out for. Take a look at these features and keep them in mind when you read our breakdowns and reviews below.

Conversion Kit Material

Conversion kits are usually made of metal, but not all metal works the same for this part. There are three main types of materials each with their own pros and cons. Take a look at these below:

Steel – steel isn’t in as much use anymore because it weighs too much and takes up too much space. In modern day receiver parts, steel is still used but only at crucial points in the conversion block.

Aluminum – as a material, this has taken over as the most common type for conversion kits. It may cost as much or more than steel, but it’s much lighter and smaller which is needed to easily fit into the existing parts. Aluminum is still tough which is needed to adapt the AR to a new caliber.

Hybrid – the hybrid conversion kit is the top of the line when it comes to the part. With most of the product made out of aluminum, they can insert steel into the crucial parts for guaranteed reliability. These parts often include the injector.

Hybrid materials made out of aluminum and steel may cost the most, but they are considered to be the best you can get. What you buy is ultimately up to you, but keep in mind what you’re looking for in a conversion kit.

Installation Process

Another big thing to watch out for when picking a conversion kits is how easy it is to install. This varies a lot that depending on the company and how they design their part.

Some conversion kits have requirements that don’t come built-in with the purchased such as adapting or Milling lower receivers to match. Others may require an additional purchase in order for the entire AR to be easily converted.

Most conversion kits are pretty clear about what requirements are needed to use their product effectively, but they don’t always advertise how easy it is to actually do the installation. The best way to find that out is to ask people who’ve actually used the product.

That’s exactly what we did in our reviews below.  In the recap section of the breakdown, we point out any consistent praise or complaints about these features for the conversion kits.


Upper conversions don’t come cheap, so you don’t have to find one that’s going to break easily.  Imagine your frustration if you dropped a couple hundred dollars on a product only to have it break a few weeks later. In our review below, we make sure to point out the features that add to the durability and long life of the conversion kits and whether or not the user experience backs up this design.


Most conversion kits are designed fit into existing parts on the AR-15, but they aren’t all designed to adapt to every 9mm magazine. Each conversion kit has their own type they work well with.

The most common compatibility is with Colt and modified UZI magazines. Other ones that show up on our list are Glock and Smith and Wesson.

Make sure to check the reviews though and the recaps for each product. Although the company may claim that it works fine with certain brands, in practice that may not be the case.

You should also check to see what upper receivers the parts are compatible with as well. You don’t want to go buy a conversion kit only to realize when you go to use it that you actually can’t use it with your current parts.


Going shopping with a clear budget in mind is always a wise choice. 9 mm AR upper conversion kits may seem to be expensive at first, but they Save-A-Lot in actually changing the function of the rifle while still being easy to switch in and out.

I recommend looking at each product with an open mind, and then thinking about what features I am willing to sacrifice for a lower price. For someone who’s planning on Switching their conversion kits back and forth, you’re definitely going to want to go for one of the premium kits, or you’ll definitely find a lot of headaches going forward.

Commonly Asked Questions

Does a 9mm AR need a gas block? – The 9mm ammo doesn’t really work well with a gas system. The smaller ammo is not usually strong enough to generate enough of the gas energy needed to engage the system, so it wouldn’t work as well.

Is a converted 9mm AR the same as a 9mm AR pistol? – No, it’s not. A converted AR, as we’ve been discussing for this specific article, is the AR rifle that fires 9mm caliber rounds. The gun is still in its rifle configuration.

A 9mm AR pistol is something different. Sure, they both fire the same ammo and use some of the same parts, but an AR pistol has a shorter barrel and uses a pistol grip. Though the AR pistol can be used one-handed, you still probably would want to use two hands as you do with any standard pistol.

Does a 9mm conversion make the AR-15 more dangerous? – It won’t be any more or less dangerous than it already is which means that it’s only as dangerous as the person that uses it.

The 9mm rounds are smaller and have less recoil which may make it more accurate when firing quickly. On the other hand, you may be losing some of its range and stopping power farther out.

If you’re asking the question about whether or not it’s more dangerous in an active shooter situation, you’re asking the wrong question. Statistically, most gun crimes are committed with handguns. Any weapon can be dangerous in the wrong person’s hands; don’t blame the weapon.


We hope you enjoyed reading about the best 9mm AR upper conversion kits. These kits can work for you and make your AR-15 something different.

I recommend the Stern Defense conversion adapter. It’s light, durable, easy to use, and it fits standard Glock and Smith and Wesson mags.

If you’re looking for something that works with Colt or UZI mags, then going with the Brownells drop-in block may be the smart choice. It comes with just enough extras to make it worth the slightly higher price you’d have to pay.

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