We love the AR-15 platform because the possibilities are endless, especially with an AR-15 caliber conversion kit.
Want to swap in a new trigger, grip, bolt carrier group, or barrel? You can! All it takes is basic tools and a little know-how. Lots of people build their own AR-15 from scratch — it’s that easy.
Changing your AR’s caliber is actually pretty simple, and we have lots of great recommendations for you.
Read on to learn more!
THE QUICK LIST
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Best .300 BLK
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Best .22 LR
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Best 9mm Conversion Kit
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Best 7.62×39
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Best .224 Valkyrie
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Best .17 HMR Conversion Kit
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Best .450 Bushmaster
Table of Contents
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Comparison Chart
| Caliber | Barrel Length | Handguard | New Bolt Required | Magazine Adapter Required | Price | |
| Palmetto State Armory .300 BLK Upper Receivers | .300 BLK | 7-16″ | M-LOK, KeyMod | No | No | $169-829 |
| CMMG .22 LR Bravo | .22 LR | N/A | N/A | Yes (included) | No (magazine included) | $164 |
| Faxon Firearms Bantam | 9mm | 16″ | M-LOK | Yes (included) | Yes | $455 |
| Radical Firearms 7.62×39 Upper Receiver | 7.62×39 | 16″ | M-LOK | Yes (included) | Yes | $433 |
| Palmetto State Armory .224 Valkyrie Upper Receiver | .224 Valkyrie | 20″ | M-LOK | Yes (included) | No | $399 |
| Bear Creek Arsenal .17 HMR Upper Receiver | .17 HMR | 20″ | M-LOK | Yes (included) | No (magazine required) | $269 |
| Bushmaster Bravo Zulu | .450 Bushmaster | 16-20″ | M-LOK | Yes | No (follower or magazine required) | $589 |
How We Tested the Best AR-15 Caliber Conversion Kits
For this article, we gathered a bunch of AR-15 caliber conversion kits we’ve personally shot, reviewed, and owned here at Pew Pew Tactical. The entire Pew Pew Tactical team, as well as freelance writers, contributed to this review to offer different opinions.
For guns we have reviews on, we’ve linked those so you can read more. Every review handgun undergoes a strict testing protocol that requires a minimum of 500 rounds of both FMJ and JHP ammo through it at 5 and 7 yards.
Meanwhile, every review rifle undergoes 500 rounds of practice ammo and heavier match-grade ammo at 50 and 100 yards with a 5-25x scope (unless otherwise noted). We require all AR-15s to be tested with at least 3 magazines to assess compatibility, and we use a Lyman Digital Trigger Gauge to measure the average trigger pull for all guns.
Best AR-15 Caliber Conversion Kits
1. Palmetto State Armory .300 BLK Upper Receivers – Best .300 BLK Conversion Kit
Prices accurate at time of writing
Prices accurate at time of writing
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25% off all OAKLEY products - OAKLEY25
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Pros
- Easy drop-in conversion
- Lots of configurations available
- Reuse your 5.56 NATO magazines
Cons
- Be careful not to mix up 5.56 NATO and .300 BLK ammo and components
Specs:
- Caliber: .300 BLK
- Barrel Length: 7-16″
- Handguard: M-LOK, KeyMod
- New Bolt Required: No
- Magazine Adapter Required: No
There’s no easier AR-15 caliber conversion than .300 Blackout. As usual, Palmetto State Armory has carbine- and pistol-length ARs for everyone.
This cartridge is specifically for suppressing and subsonic rounds are widely available.
A .300 Blackout upper will use the same bolt carrier group, magazines, buffer, and more.
Converting to .300 BLK is easy, but it’s so similar to 5.56 NATO that there are some safety concerns. It’s easy to get the two mixed up if you aren’t careful.
While you can use standard 5.56 magazines with .300 BLK, you may want to invest in dedicated .300 Blackout magazines. Either way, mark them so you don’t grab a mag full of the wrong ammo and blow up your AR.
And for more, check out our guide to the Best .300 BLK Uppers.
Prices accurate at time of writing
Prices accurate at time of writing
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25% off all OAKLEY products - OAKLEY25
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What’s your take on .300 BLK ARs?
2. CMMG .22 LR Bravo – Best .22 LR Conversion Kit
Prices accurate at time of writing
Prices accurate at time of writing
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25% off all OAKLEY products - OAKLEY25
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Pros
- Take advantage of cheap ammo
- Everything you need is included
- Great for new shooters
Cons
- Rimfire ammo is dirty and finicky
Specs:
- Caliber: .22 LR
- Barrel Length: N/A
- Handguard: N/A
- New Bolt Required: Yes (included)
- Magazine Adapter Required: No (magazine included)
If you want to save money on your live-fire training, there’s nothing better than shooting .22 LR. It’s practically free!
You can buy a dedicated .22 LR upper, but let’s keep things as affordable as we can. Who’s trying to spend a ton of money to save some money?
A .22 LR conversion is the cheapest conversion you can do to a 5.56 NATO AR-15. It allows you to shoot budget-friendly ammo that’s perfect for practicing skills and training new shooters.
Because the .22 LR is nearly the exact same diameter as 5.56, you don’t need to swap your barrel, upper, gas system, magazine well, or anything crazy like that. All you need to do is swap out the bolt carrier group.
The CMMG system offers a built-in buffer system and replaces your standard BCG. It comes with a single magazine, and spares are readily available.
As a one-piece system, the CMMG bolt is perfect for quick swaps and range trips. The CMMG bolt works surprisingly well, and I enjoy it.
The magazines are affordable, but I never needed more than two for my shooting.
There’s only one downside: .22 LR ammo is very dirty. The stainless steel bolt wipes clean easily enough, but you’ll have more cleaning to do than you would with 5.56 NATO.
The conversion makes the gun a blowback design so it’s reliable in both direct impingement and gas piston guns.
Prices accurate at time of writing
Prices accurate at time of writing
-
25% off all OAKLEY products - OAKLEY25
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Check out more of our favorite AR-15s in .22 LR!
3. Faxon Firearms Bantam – Best 9mm Conversion Kit
Prices accurate at time of writing
Prices accurate at time of writing
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25% off all OAKLEY products - OAKLEY25
Copied! Visit Merchant
Pros
- Cheaper ammo
- You probably have magazines already
- PCCs are practical
Cons
- Requires more specialized parts
Specs:
- Caliber: 9mm
- Barrel Length: 16″
- Handguard: M-LOK
- New Bolt Required: Yes
- Magazine Adapter Required: Yes
Without a doubt, one of the most popular conversions for an AR-15 is 9mm. It’s the most popular centerfire pistol round and the Faxon Firearms Bantam is a great complete upper for your AR-15.
As a PCC you can use it in most indoor ranges, as well as compete in USPSA PCC division. 9mm ammo is pretty cheap (outside of ammo shortages) and a bit more fun to shoot than a rimfire round.
A 9mm AR doesn’t run off the same direct-impingement or piston operating method as a 5.56. Instead, most utilize a direct blowback-style operating system. This makes them simple and relatively affordable.
You will have to modify your lower receiver to shoot 9mm, but it’s not difficult and you can easily reverse these changes.
Stern Defense makes magazine well adapters for Glock, S&W M&P, Beretta 92, and SIG P320 magazines.
Prices accurate at time of writing
Prices accurate at time of writing
-
25% off all OAKLEY products - OAKLEY25
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You should also look into a heavy buffer and buffer spring to keep your AR-15 cycling smoothly.
Check out our CMMG Bantam PCC review and even more of the Best 9mm Uppers if you want to get into the world of pistol caliber carbines.
Prices accurate at time of writing
Prices accurate at time of writing
-
25% off all OAKLEY products - OAKLEY25
Copied! Visit Merchant
4. Radical Firearms 7.62×39 Upper Receiver – Best 7.62x39mm Conversion Kit
Prices accurate at time of writing
Prices accurate at time of writing
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25% off all OAKLEY products - OAKLEY25
Copied! Visit Merchant
Pros
- AK ballistics from an AR platform
- Ammo is (usually) cheap
- Minimal changes required
Cons
- You'll need new magazines
Specs:
- Caliber: 7.62×39
- Barrel Length: 16″
- Handguard: M-LOK
- New Bolt Required: Yes (included)
- Magazine Adapter Required: No (magazines required)
While the AR is nearly the polar opposite of the AK in terms of rifle design and philosophy, it’s pretty easy to convert your American AR into an instant Vodka fan with this Radical Firearms 7.62×39 upper.
The 7.62×39 cartridge is an excellent round for inside of 300-meters (remember, we’re on the metric system this time). Inside an AR-15, it’s decently accurate and a real close-quarters hammer.
Check out our Best 7.62×39 Ammo guide for some of our faves.
For a long time, it was tough to convert an AR into 7.62×39 and make them run reliably, but these problems are mostly smoothed out now.
This complete upper is ready to rock. All you need are some new magazines. The 30 rounders are straight goofy but the 20 rounders look a bit more normal. You want to go for quality with these magazines so opt for C-Products and D&H.
Prices accurate at time of writing
Prices accurate at time of writing
-
25% off all OAKLEY products - OAKLEY25
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Lastly, you may or may not need some trigger work.
The primers in Russian ammo are often quite hard, so you may need an extra power hammer spring from Wolf to make sure they keep kicking off.
Experiment first, and then see if you need a little more oomph.
Prices accurate at time of writing
Prices accurate at time of writing
-
25% off all OAKLEY products - OAKLEY25
Copied! Visit Merchant
5. Palmetto State Armory .224 Valkyrie Upper Receiver – Best .224 Valkyrie Conversion Kit
Prices accurate at time of writing
Prices accurate at time of writing
-
25% off all OAKLEY products - OAKLEY25
Copied! Visit Merchant
Pros
- Excellent long-range performance
- Low recoil
- May work with your existing magazines
Cons
- Expensive ammo
Specs:
- Caliber: .224 Valkyrie
- Barrel Length: 20″
- Handguard: M-LOK
- New Bolt Required: Yes (included)
- Magazine Adapter Required: No (magazines required)
We’ve had a ton of shooting .224 Valkyrie long-range, and Palmetto State Armory makes a great upper for budget-conscious shooters.
We’ve talked about .224 Valkyrie quite a bit here at Pew Pew Tactical.
It’s a short-action round designed for long-action performance. Best of all it uses parts that are all already in circulation for the fabled (and failed) 6.8 SPC.
This upper from PSA is all about going the distance. It comes with a heavy-contour stainless steel barrel that will stay cool and on target longer than your run-of-the-mill AR-15. Stick a bipod under this thing with the M-LOK rail and get ready to shoot further than you ever did with 5.56 NATO.
Prices accurate at time of writing
Prices accurate at time of writing
-
25% off all OAKLEY products - OAKLEY25
Copied! Visit Merchant
Some 5.56 magazines will work, but 6.8 SPC magazines are pretty affordable and accessible to find.
If you build your own, you’ll need the parts listed above and a 6.8 bolt, but you can use a standard bolt carrier group.
The .224 Valkyrie is a bit Gucci right now so expect to pay a pretty penny for the parts and the ammunition. It’s still a fun round that’s extremely accurate, but also soft-shooting and fun.
Prices accurate at time of writing
Prices accurate at time of writing
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25% off all OAKLEY products - OAKLEY25
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Read our full PSA .224 valkyrie review for all the info!
6. Bear Creek Arsenal .17 HMR Upper Receiver – Best .17 HMR Conversion Kit
Prices accurate at time of writing
Prices accurate at time of writing
-
25% off all OAKLEY products - OAKLEY25
Copied! Visit Merchant
Pros
- Is this the perfect varmint upper?
- Heavy-contour barrel
- Awesome rimfire accuracy
Cons
- More expensive than .22 LR ammo
Specs:
- Caliber: .17 HMR
- Barrel Length: 20″
- Handguard: M-LOK
- New Bolt Required: Yes (included)
- Magazine Adapter Required: No (magazines required)
I love .17 HMR. It’s super accurate, surprisingly powerful, and easily one of the best rounds for taking small game and even medium-sized predators — especially with this upper from Bear Creek Arsenal.
You can make your AR a .17 HMR tack driver through one of the coolest conversions ever. This upper has a heavy-contour barrel that will happily put tiny .17-caliber rounds on target all day long.
Of course, you’ll need a new magazine.
I own a .17 HMR AR-15 and love it.
Prices accurate at time of writing
Prices accurate at time of writing
-
25% off all OAKLEY products - OAKLEY25
Copied! Visit Merchant
7. Bushmaster .450 Bushmaster Upper Receiver – Best .450 Bushmaster Conversion Kit
Prices accurate at time of writing
Prices accurate at time of writing
-
25% off all OAKLEY products - OAKLEY25
Copied! Visit Merchant
Pros
- Hits like a freight train
- Easy conversion
- Uses AR-15 magazines (with a new follower)
Cons
- Harsh recoil
Specs:
- Caliber: .450 Bushmaster
- Barrel Length: 16″, 20″
- Handguard: M-LOK
- New Bolt Required: Yes (included)
- Magazine Adapter Required: No (follower or magazine required)
If you just wish your AR-15 had way, way more stopping power, this Bushmaster conversion kit has your name written all over it.
The .450 Bushmaster cartridge is a hoss, but it fits inside AR-15 magazines and works with standard lower receivers. Might want to invest in a tough optic, and maybe some ice packs, because the recoil takes a toll on optics and shoulders alike.
Since Bushmaster developed it for the AR-15 platform, converting is as easy as dropping the supper onto your current lower.
Prices accurate at time of writing
Prices accurate at time of writing
-
25% off all OAKLEY products - OAKLEY25
Copied! Visit Merchant
If you need a sledgehammer of a hunting rifle or just like slinging big chunks of lead (nothing wrong with that), step up to the plate and give this fella a swing.
How to Pick the Best AR-15 Caliber Conversion Kit
Why would I want to convert my AR-15? Why not just buy an entirely new rifle?
First of all, it’s cheaper. You also don’t have to go through an FFL to make your purchase since it’s the lower receiver that the ATF considers a firearm; the upper receiver is just an assembly of parts.
And shooting more calibers is good, clean fun!
I convert between different calibers based on my use case. I swap to .22 LR when I’m bored or want to train new shooters and run .17 HMR when I hunt rabbits or coyotes.
You might have a feral hog problem that calls for something heavier than 5.56 NATO. Maybe you want to train on mute with subsonic .300 BLK and a suppressor. Perhaps you have a bunch of 9mm ammo and want to train with that instead of more expensive rifle ammo.
They’re all valid reasons to convert your AR-15 to a new caliber!
The key is to identify your needs, find a suitable cartridge, and look for a conversion kit that fits the bill.
Meet the Experts
Pew Pew Tactical writer Travis Pike authored this article. Travis spent a lifetime shooting as a kid and later joined the United States Marine Corps, where he spent five years as an infantryman. In the middle of his Marine Corps career, he began writing and never stopped. Travis is an NRA-certified instructor and Concealed Carry Instructor for the state of Florida. He has thousands of articles to his name with a variety of publications, including Pew Pew Tactical.
Editing this article is Scott Murdock. Scott is a Marine Corps veteran who competed and qualified as a rifle and pistol expert while in service. In addition to shooting, Scott has written for a variety of publications, testing, researching, and evaluating guns and gear. He brings that knowledge and skillset to this article, editing and fact-checking for accuracy.
Editor-in-Chief Jacki Billings runs our experienced team of reviewers. She is a National Rifle Association Basic Pistol Instructor as well as a member of the Society of Professional Journalists, ACES: Society for Editing, and the Professional Outdoor Media Association. Jacki has a bachelor’s degree in journalism and has worked as a media professional for close to 20 years, specializing in gun media for almost 10 years. With 2,000+ articles to her name, she uses her professional journalism and editing experience to set testing protocols and editorial standards for Pew Pew Tactical.
Final Thoughts
The AR-15 is a brilliant design and a testament to that is just how far people are pushing it.
Its ability to swap calibers is fantastic and useful for those that want one rifle that can basically do it all.
Have you guys done any converting? If so, what? Let us know below. For more great AR-15 content, take a look at our Definitive AR-15 Guide!
Latest Updates
April 2025: Added the .450 Bushmaster conversion kit. Removed the Brownells 9mm adapter and Colt magazine combo.
39 Leave a Reply
Notably absent...6.5 Grendel???
.50 Beowulf. One hole groups, and it's a powerhouse too.
ka-BOOM! Good recommendation.
What about 6ARC... clear the room then LPVO it out to 900 meters in a 14 in bbl configuration. About 350 ft lb of knockdown at 900 meters from a CQB bbl -- good for 2 legged varmits shooting 7.45 x 39 at ya.... don't punch their level 4 armor.. go for appendages.. takes 4 guys to help one. ... - force divider! .. plink em all day long. I think this is where the US Military should go....
I have many conversions, 45ACP, 40 S&W, 9mm, 22LR, 300 BLK, 450 Bush (which I haven't shot yet), but has anybody ever heard of anybody making a .38 special, .357 mag or 44 mag AR barrel? I just looked up Olympic Arms and they are out of business, oh and I got a 10mm barrel upper and special magazine from them years ago, never shot it yet, I know I'm crazy but hey, I'm retired so have more money than sense right now!!! Holler back!!!
I was hoping to see more options for hunting? Why aren't the other calibers discussed here (i.e.6.5)?
I was hoping to see more options for hunting? Why aren't the other calibers discussed here (i.e.6.5)?
i have 3 x ar 15s in 7.62x39
2 x 16.5 carbines and 1 x 10.5 pistol
i use mil spec hammer springs enhanced firing pins and 28 round c products magazines in all of them
theyre stone cold reliable with tula ammo
and accurate too
the one carbine recently put 5 tula fmjs in a group just under two inches at 200
yards with a primary arms 1-4x arms on top and a psa ept trigger in the lower
all 3 uppers are from bear creek arsenal
250 bucks shipped includes nitrided bcg mlok rail and cnc billet upper receiver
Same here but 1 and 1 both side changed ar15 in 762x39 worthy price!
I love PSA, but BCA is where it's at. I own several BCA uppers, my favorites are my 7.62, 22lr, and my AR 10 243, all reliable shooters and 100% made in the USA!
no 0.50 Beowulf?
I converted to 300 Black out.also 450 Bushmaster,Both give great accuracy. I really like the 450 for Deer and Hogs.I only use 5.56 for varmints or just for fun at the Range to practice my trigger pull and safe gun loading and accuracy. The AR is a great platform to Build on.
After an unimpressive experience with an M16 in 1975, I wasn't interested in AR's for a long time. My prairie dog hunting {and other nefarious activities} buddy kept after me. My favorite phrase of his on the subject was "you know, it's been 40 years". There's a great story behind how I finally made the actual purchase, but I'll save that for another time.
After having used my Ruger SR15 VT on a couple trips to the dogtowns, and loving it very much, my buddy told me about the Sharps Rifle Company .25-45 Sharps. For the price of the upper, I could change to a caliber that among other things, would be legal for deer in MN, where I live. Another huge advantage in my mind was the ability to make brass from 5.56 NATO or .223 REM brass. But at the time there was no load data for the .25-45 Sharps!
Being a stickler for, um, just about everything, I buckled down for the process of working up my own load data. I've reloaded for years, and so was confident in the fact that I better keep my healthy paranoia going or I'd end up with a really nice new upper that was totally useless and funny looking to boot.
I started looking at other calibers made from 5.56/.223 cases, 6mm & so forth. I checked case capacities and load data, and finally loaded up 5 loads from 23.5 grains to 26 grains of powder, 5 rounds of each. Then I shot them at 100 yards, looking for pressure signs all along the way. The groups went from fairly open to smaller & smaller, with the smallest being at 25 grains, and then at 25.5 grains it started to open up again. I confirmed this over & over, and 25 grains of that powder is what I load to this day. And that's the same powder charge I use for 5.56/.223, very handy.
I've always liked the smallest load needed to accomplish the task. They are more accurate, cheaper to load, and easier on equipment, and they allow for a safety margin. Working up that load for my first AR conversion is the most fun I've had reloading, and possibly shooting too, in my entire life!!!
Got 300 blackout and a CMMG 22lr conversions. Love them both. Neither one is a tack driver. But since the 300 is a CQC self defense weapon and the 22lr is just plain fun to shoot I don't need that type of accuracy
I need one place that I can get a complete ar9mm converson upper,big,mag block. No piece meal.
No .458 socom?!
Looking for a AR 410, upper receiver?
Garrow....what happened to them? I looked them up, nothing available plus a lot of unhappy customers who claim to have paid for their orders and never received the product?
CMMG .22LR conversion, in an AR with a properly sighted 1-6x optic.
What is the likely impact change, vs 5.56/.223 - 55/62gr on 50yds and under targets?
Probably minimal, but you should test to make sure.
The CMMG kit sucks ass. Much better off having a separate 22 like the 10/22 with upgraded trigger.
I tried the CMMG kit and it did not work in my AR. I have a custom trigger in the AR which may be the problem with the fail to fires. Doesn't matter what type of 22 lr ammo used. The custom trigger is 2.5 lbs.
Many lightweight triggers have issues with light striking CMMG kits. That isn't really the fault of the CMMG kit and is just one of the design limitations that you have to work with.
I thought this was going to be an article on the QCB (quick change barrel kits) available. I'm in the process of doing T&E of three or more of them. I'm not interested in the Pantheon Arms Dolos.
For 9x19mm, you pretty much need a separate upper as it uses a different BCG. For .223 Wylde, you can use a QCB to convert it to anything that uses a standard 5.56mm NATO BCG and do .22 LR with the CMMG .22 LR conversion kit which gives you .300 BLK. I've pretty much decided I want the KAK Industry 6¼" Baby Blond barrel. However, I want to try the RightToBear 6" and V Seven 6½" barrels. I think around 6" is the sweet spot for .300 BLK AR pistol barrel lengths especially if you're going to run suppressed.
I've pretty much decided to standardize on Aero Precision uppers.
Is there a reason the 204 Ruger dint make your list? It is a high velocity, highly accurate round that is a necked down 223 casing. Just curious, as you have a laundry list of calibers that require more than just an upper swap. I mean some of these your changing out to different mags or converting the mag well and having to swap out spring rates to allow for proper cycling of the AR without damaging it.
Just curious.
No reason against it! .204 Ruger is just a fairly niche cartridge and uppers can be a bit hard to find. It will definitely be looked at when we update this article though ;)
6.5 Grendel Man,6.5 Grendel.
Beat me to it.
.243 WSSM in 55 grain will run 4170 FPS and is perfectly suited for the short action AR platform.
Heavier bullets will anchor a deer at extremely long ranges.
Beowulf ? ?
I just can’t believe you left out the 6.5 Grendel. Arguably the best option regarding the article. However, mistakes happen and I know you’ll get it right next time.
I thought the same thing. 1 sentence at the end lumps together the popular calibers.
6.8 SPCII has a tighter chamber and turns your AR into a sweet little deer rifle. 358 Yeti (wildcat) is another caliber using cut down .308 brass and sends a 200 gr pill downrange at 2400+ fps. Bit more of a kick but it drops anything it hits. Details on FB.
Plus a fantastic hog killer. The caliber of choice for feral hogs.
Excellent article, I love the AR platform and it has infinite variables.
I can't believe you would leave out the 6.5 Grendel! An amazing round that will take out medium size game with low recoil, excellent distance and maintains good fps out of a 12" barrel It is on fire at our gun club currently most purchased caliber. What gives?
22 noseler is a good round a barrel change and 6.8 magazines gets you down rang fast and far good for target and critters,ammos hard to fing and expensive but if you have 556&black out its another option.
To my knowledge the PSA KS-47 7.62x39 upper requires a PSA KS lower. You can’t just swap it onto a standard AR lower and be good to go.
"But, they require a proprietary lower – so it isn’t a true conversion"
The author covered that.
Why put it in at all???? It’s a platform onto itself and is no conversion at all. It doesn’t fit with the subject matter. Might as well mention mutants which have been around much longer or S&W’s dedicated 22LR AR.
The popular calibers were barely mentioned as an afterthought. 17HMR?? Probably the least popular conversion done.
This being said this article was 1000% better than the “humor” articles.