Best AR-15 Conversion Kits (2022): Reviewed

Best AR15 Conversion Kit Feature Image

There have been plenty of changes in the popularity of various ballistics types and it have been quite constant for the past few years. The modularity of guns like the AR-15 makes it relatively easy to convert the rifle to a different calibre, which is considered a rather simple process.

Let’s establish the fact that no two ARs are the same first. You can easily swap almost every single AR-15 parts for something that is different. The AR-15 is an exciting piece of firearm history and over time it has only become a better weapon for a lot of gun owners.

An AR-15 can be made for close distance shoot-outs with a 7.5-inch barrel, or a long-range precision with a match grade 20 inch rifle. You can also choose to swap grips, triggers, stocks and any other parts. One other thing you can do is easily is to convert your AR-15 to a variety of other calibres.

Most of AR-15s come in the classic 5.56 NATO rounds. Meaning to say, this little fellow was what the AR-15 was designed to function with. And it is often the most affordable option for new AR owners, so to speak.

With all that being said, you may have a different calibre of AR-15, however, it is more than likely that you will be able to convert your AR-15 into a wide variety of different calibres.

Conversion KitsNameEditor’s CommentRatingGet The Best Deal
ATI AR15 9mm Adapter for 5.56 Lower Receivers

Most Recommended Option

1. Allows for a quick conversion to 9mm
2. Made from 6061-T6 Aluminum
3. Has a bolt hold open feature

Stern Defense Mag AD91. Constructed from 6061 T6 aircraft grade aluminum
2. 4140 NiB coated feed ramp
3. Hard coat anodized type 3
9.5/10SHOP NOW
Brownells AR15/M16 with 32 Round Magazine Conversion Block1. Allows for a quick conversion to 9mm in conjunction with a 9mm upper
2. Allowing for a quick and easy change of calibers
3. No need to swap out the standard hammer, if using 100-004-363 9mm bolt carrier
9.0/10SHOP NOW
Hahn Precision AR15/M16 Conversion Block1. Machined aluminum block converts AR-15 lower receiver to 9mm
2. Compatible with all, Colt-type, 9mm upper receivers
3. Roller retention device holds block securely in receiver
8.5/10SHOP NOW
Rock River Arms AR15/M16 Conversion Block1. Steel with matte black oxide finish
2. Aluminum with matte black, hardcoat anodized finish
3. Fits CAR-15/M4 collapsible stock models with .154″ diameter receiver pin holes
8.5/10SHOP NOW
Colt AR15/M16 Conversion Block1. Well adapter converts standard AR-15/M16 lowers for use with Colt 9mm upper receivers
2. Accepts Colt 9mm style magazines
3. Includes ejector and feedramp
8.0/10SHOP NOW

Reasons To Convert : AR 15 To 9mm Conversion Kit

You may have questions about converting a perfect AR-15 rifle. Why should you? And why swap out any of its parts to begin with? Anyone can just buy a new rifle instead of converting it, and so can you.

They are all pretty good and solid questions and thinking, and you are more than welcome to do that. Every gun owner will have questions regardless of what area it is. However, there are many equally solid and great reasons to use a base gun to swap calibers too.

A lot of American states charge fees and put ridiculous waiting periods to buy a gun as we speak. In other possible situations, it is all about keeping that one perfect lower receiver.

The majority of your rifles’ controls are in its lower receiver. That US$200 adjustable trigger can also be used for more than one caliber, as does that B5 stock, along with the Magpul BAD lever. Throw in those Ambi-safeties and magazine releases too, and your AR-15 will be looking and working well in no time!

A lower stock is not hard to walk away from, in all honesty. However, that lower stock you have invested some real money in will be a great host for many conversions.

Feel free to choose whether if you want to convert your AR-15 to a 9mm or not. Your reasons are pretty much your own.

The 9mm is, without a doubt, one of the most popular conversions for an AR-15 rifle. As the 9mm is the most popular centrefire pistol round, it is also an excellent round for the AR-15. Should you know – a 9mm AR-15 does not run off the same gas system as a 5.56 and, at the same time, is a blowback style weapon.

Advantages of a 9mm Conversion Kit

There are a few factors you will enjoy when you choose to convert your AR-15 to a 9mm through conversion kits. Here are some of the reasons you will be.

One of the reasons is the lower the cost of ammunition. For obvious reasons, you are going to put this into a different use. However, shooting a 9mm is going to save you a bit per shot.

The other reason is the muzzle blast and noise. The smaller the caliber is, it is going to lessen the noise. It may even make it just a little more comfortable to shoot for you as a gun owner too.

If you have to compare it to shooting with a pistol, then you will find that you will gain a bit more range and speed when shooting with an AR-15. There are obviously other, more potent options for shooting a 9mm. However, if you like the AR-15 platform, then there is no harm in that. After all, it is a decent choice.

Last but not least, if you find it useful to stock up on one type of ammo, then choosing a 9mm may serve you quite well. It’s cost and versatility make it a very good choice when you want to have a solid supply on hand for various uses in case of SHTF scenarios.

The Difficulty Level of  the Conversion

Being a leader of modularity, the AR-15 definitely deserves the nickname of the “Lego of the firearm world”. Any gun owners and gun users will know how easy and convenient it is to make changes and adjustments to the gun and even add a limitless array of customization too.

As gun owners, you can choose from several conversion kits for converting a mil-spec AR-15 to a 9mm. The most convenient way is to change the upper assembly out for another completed upper receiver.

You can also just use a conversion kit that replaces the bolt carrier group. The first and more extensive approach infers a candid drop-in to fit your Lower Receiver. This set usually contains an upper assembly, which includes a barrel and a magazine well adapter. It can cost anywhere from US$700 to well over US$1000.

The other way to do it means using the AR-15’s standard upper receivers. You can convert to a 9mm Parabellum calibre by fitting a new barrel, a new bolt, and a magazine adapter to it.

What Tools Do You Need?

If you wish to build a 9mm upper receiver with a conversion kit, it is considered a very simple operation if you are comfortable with just a few basic tools. To replace the bolt carrier group and buffer, and then inserting the block into the magazine well, you will need a barrel nut wrench. At the same time, you will also need a receiver vice block to help you out with the conversion job.

What Parts Do You Change?

According to quite a number of gun users, using a conversion kit really does work out to be more affordable most times. Even then, it usually is more affordable than buying the pieces individually and separately.

Separate pieces’ prices fall into different price points for obvious reasons. It usually costs around US$200 for a bolt; the 9mm barrel will cost you another US$150 to US$200. At the same time, the magazine block may cost you another US$50 to US$200, and the heavy buffer and heavier buffer spring may cost you around US$50 to US$75.

Unlike the AR-15’s regular 20 inch barrel, the pistol-caliber carbine usually features a 16-inch barrel. It may even be a lot shorter too. They may even have straight magazines with a 10 round or a 32 round capacity. There are also 50 round and 100 round drum magazines.

However, ownership of magazines with more than 10 rounds and a barrels length of less than 16 inch is illegal in some states. Hence, it is best to check with your state laws to see what specifications are legal.

The Process of the Conversion

The installation of the 9mm barrel is similar to any other barrels and can be done without gunsmithing assistance or other similar modifications. Since the back of the barrel is in the same diameter and shape, and the barrel nut is the same, all you need to do is just turn the barrel nut and finish it with the handguard of your choice.

Just remember that the 9mm barrel has different threads at the muzzle than the .223/5.56 to prevent you from installing an inadequate flash hider on your AR-15 9mm barrel.

The massive one-piece bolt is a blowback type and replaces the standard two-piece .223/5.56mm bolt. While it uses the same charging handle and buffer, for the best performance you should install the heaviest buffer.

Another modification you can make to the AR-15 rifle will have to be using a special adapter to allow the use of smaller 9mm magazines. There are 2 kinds of conversion blocks – one inserted from underneath and held in position by the magazine catch. The other one is from the top, held in by some bulge and lips. It is highly commended to use the conversion adapter drop in from the top.

The barrel lengths range from 16 inches for carbine conversions to pistol barrels, which are just 3 inches long!

The Best AR-15 9mm Conversion Kit – Reviewed

Now that we are done with some of the basics, here are our top picks for the best 9mm conversion kits that are currently on the market.

1. Stern Defense Magazine AD9

Stern Defense MAG-AD9


The Stern Defense MAG-AD9 is considered to be in the more expensive level of all AR-15 Conversion Kits. It is originally made from lightweight 6061 T6 aircraft-grade aluminum and it is now made from 4140 alloy steel.

This 9mm AR-15 adapter allows the Glock-style double stacked 9mm or .40 S&W magazines to be used with no excessive needed modifications to your lower or magazines.

The Stern Mag AD9 series adapters also come with a last-round hold-open feature and built-in magazine release for Glock-type magazines. Its latest version that boasts the magazine release is upgraded to be flushed with the magazine. It has been made to be functioning well without the bulge that was present in the previous magazine latch.

These adapters really need the use of a Glock cut bolt. However, depending on your bolt selection you may have to trim a little off the top and the sides of its ejector.

With the accustomed AR-15 plug-and-play system, the Mag AD bottom-fed magazine adapters can be installed in a matter of seconds in any mil-spec AR-15, M4, or M16 lower receiver. You can, in turn, turn it into a Glock magazine-fed lower. If you choose to use the Stern Defence adapter, you will get to keep all of the gun’s stock components – except the barrel and bolt.


2. Hahn Precision AR-15/M16 Conversion Block

Hahn Precision AR15 M16 Conversion Block


The Hahn Precision AR-15/M16 9mm Drop-In Conversion Blocks comes in 2 versions. It all depends on the direction of mounting the block to the lower receiver.

Hahn Precision offers you as a gun owner both bottom-loading and top-loading adapters. The bottom-loading magazine adapter obviously inserts from the bottom of the lower receiver and secures with a non-marring tension feature. That way it prevents any accidental release.

On the other hand, the Top-Loading Block, which drops in from the top of the lower receiver, requires the removal of the bolt release. The drawback is that it will not be swappable in the field.

The Hahn one-piece Conversion Blocks are made from aluminum billet and are well-matched with all Colt-type and modified UZI magazines. The adapter also boasts a last-round hold-open feature on a top loader. There are 2 kinds of the bottom loader – with and without the hold-open device.

The bottom-fed magazine adapter without the built-in hold-open needs an extended catch to hold open on the last round. It is said to be weaker than the .223 version, and it can break easily during extensive and excessive use.

The 3rd bottom-loading adapter has a built-in standard 5.56mm bolt hold-open functioning in conjunction with a feed ramp. It is made for reliable feeding with all types of bullets, including hollow point and frangible ball loadings.


3. Rock River Arms AR-15/M16 Conversion Block

Rock River Arms AR15 M16 Conversion Block


Another conversion kit that comes to mind is the Rock River Arms. It uses the Colt-style system which is very popular since they are half the price of a genuine Colt.

The Rock River Arms 9mm magazine block is inserted up into the magazine well and is held by the standard magazine catch. You can also use it with the standard Uzi magazine – but without the bolt hold-open feature.

The Rock River Arms Conversion Block is a drop-in solution made from aluminum and steel and it fits a mil-spec small pin (.154″ dia.), .223 lower receiver. This bottom loader uses a set screw to secure the magazine block, which enables the magazines to use the standard magazine catch. The RRA conversion block will only be able to hold open with Colt and modified UZI magazines.

The only criticism of this slightly more affordable setup is that with UZI magazines, the follower’s angle is too steep. That means that the bolt will not strip the last 1-4 rounds out of the magazine too frequently.


4. Colt AR-15/M16 Conversion Block

Colt AR15 M16 Conversion Block


The original Colt 9mm AR-15 magazine well adapter changes the standard AR lowers itself to use Colt 9mm style magazines. This bottom loader uses the normal AR-15 bolt catch and comes with a last-shot hold-open feature.

This conversion block is made from rugged aluminum, and the funneled magazine well ensures smooth entry of Colt-style 9mm magazines. Its feed ramp with a steel insert has been heat-treated for consistent round delivery with the majority of bullet types.

This block for the AR-15 installs pretty quickly and easily by using a setscrew to lock down and secure it.

The main disadvantage of the Colt conversion block is its more expensive magazines compared to the other block-style surplus kinds.


5. Brownells AR-15/M16 Conversion Block (32 Rounds)

Brownells AR15 M16 - 32 Round Magazine Conversion Block


The Brownells AR-15 Drop-in conversion block is considered one of the more expensive adapters. However, it also comes with a Colt-style 32 round magazine.

This adapter, which is made from an aluminum block and hardened steel ejector, converts your standard AR-15 model into being able to accept the Colt-type magazines.

The Brownells conversion block is compatible with almost any Colt-type, 9mm upper receivers while the feed ramp is made for reliable feeding of all types of ammunition. That includes hollow-point bullets too.

A spring-loaded roller retention device upholds constant tension against the lower receiver well to prevent the accidental release or free play. Unlike Colt magazines, this Brownells bottom-loading model effortlessly utilizes a BHO feature. However, modified UZI magazines last-round-hold-open will most likely not work.

According to a lot of gun owners, this conversion block is relatively easy to install into an existing AR-15 lower receiver. When it is put together with a 9mm bolt carrier group, there is no need to change the standard hammer.


6. ATI AR-15 9mm Adapter 5.56 Lower Receiver

ATI AR15 9mm Adapter for 5.56 Lower Receiver


The AR-15 to 9mm adapter from ATI has been made from 6061-T6 aluminum. It also fits any standard 5.56 lower receiver pretty well, so to speak. The adapter features a built-in magazine release, which is suitable for Glock-style 9mm magazines.

The adapter slides inside the magazine pretty well of the upper receiver, just like any normal AR-15 magazines will do. The bolt’s hold-open feature in the adapter locks the bolt in place safely after the last round is fired. That is a good safety and operational measure to have.

The adapter works with Glock double stack-style magazines. Furthermore, it comes with a 10 round 9mm magazine, which is included in the package. The adapter has been machined from aluminum. Hence, it is durable and strong enough to withstand a lot of shocks and pressure.

The bottom line is that the ATI AR-15 9mm adapter features a robust and simple design to convert your AR-15 into a 9mm rifle almost immediately. The adapter is comparatively less pricey than some of its equivalents, however, it may still need some fitting to eliminate play.


Our Verdict

For the regular gun owners, conversion kits are great alternatives which allow gun owners to switch from using a 9mm ammo in a handgun to a rifle that affords versatility. Besides that, pistol caliber carbine works well as home-defense rifles.

They are also great as plinking guns and training rifles for adults as well for young gun users. If you are ready to get a conversion kits, it is not a hard adjustment – just give it a try!

Frequently Asked Questions (FAQs)

Can the 9mm modification be converted back easily?

Yes you can, of course. Changing the 9mm modification is as easy as mounting one. All you need to do is to pull out the modification from the magazine well, take out the two takedown pins, change the upper, put back the pins, and you are pretty much done.

The 9mm modifications were designed to save you time and money. It prevents you from having to buy a completely new AR-15 chamber for the 9mm.

The mods here are so simple that it is less likely that you will ever need a gunsmith to help. If you know how to separate the upper and lower receiver, then you can apply and remove the mod within a matter of seconds. However, if you do not know how it works, it takes only a couple of minutes to learn.

The 9mm modifications are just plug-and-play devices. You can even shoot a 9mm from a 223 platform without changing the upper receiver. However, it is still not recommended. So most of the time spent in changing the modification is changing the upper receiver fit for the 9mm caliber. That usually amounts to approximately 30 seconds.

How To Convert AR15 to 300 Blackout?

Firstly, you’d need a .300 AAC Blackout barrel to begin with. The upper magazine, lower magazine and gas system of a .223 AR 15 are usually compatible with a 3.00 Blackout so the only conversion kit part that you really need is to get the barrel. Once you’ve the .300 Blackout barrel, just remove the .223 barrel and install the other barrel as per usual and you’re good to go!

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