While the gold standard for AR-15s has always been and likely always will be the 5.56 NATO cartridge, one of the best things about the AR platform is that it is just so darn flexible.
From .22 LR to .50 cal heavy weights, the AR can support a lot of flavors of cartridges. Most of the time, all it takes is a new upper and some new mags.
With so many options out there, we’ve broken it down to the most common (and some weird ones) to get you off on the right track.
The Quick List
- .300 AAC Blackout (.300 BLK)
- 6.5 Grendel
- 6.8 SPC
- .458 SOCOM
- .50 Beowulf
- 6mm ARC
- .22 LR
- 7.62x39mm
Table of Contents
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How to Choose an Alternative AR-15 Cartridge/Caliber
Choosing a rifle cartridge isn’t as simple as just picking the one that’s the most powerful or the coolest.
Picking the right rifle cartridge can change almost everything about the characteristics of your rifle.
The basic categories to choose a cartridge involve compromises of power, cost, and usefulness…just like deciding on the perfect car.
- Power: This is the biggest balancing act and involves the most real-world experience.
- Flexibility: A feature that sounds great in theory but can be hard to pull off.
- Availability: More is always better here, consider not only the supply but also the demand.
- Cost: Cheaper is always better, the cheapest rounds tend to be the best and most widely used.
Pursuit of Power
The power of the cartridges involves two main types of power: penetration and velocity. It may seem like these two types are the same thing. While they are related…they are two different beasts.
Defining the exact power of a cartridge is hard to nail down in a scientific sense. Numbers such as the kinetic energy of a round can tell you a lot about a round but it’s certainly not the only important thing.
You can think of the velocity of the bullet like the engine on a truck. It produces all the power/force necessary for the truck to move, but the transmission is what connects the engine to the wheels.
Without the transmission, the truck won’t get off the line. Bullet weight is the “transmission” that causes penetration.
Velocity is a great thing but without an adequately heavy bullet, velocity is irrelevant. Bullet weight is what causes penetration and lethality.
Cartridges that throw heavy bullets at medium velocities are more powerful than a lighter bullet traveling faster because light bullets lack the ability to penetrate and cause damage.
Just like you wouldn’t use a Ford Fiesta to move a boat you wouldn’t get in an 18-wheeler to drive to work. The balance of power is the key.
Depending on what you’re shooting at you may need far less than you think.
Flexibility
If you’re on a budget, just getting started, or just want an all-around gun, flexibility is important.
I realize this is a pretty nebulous term because no single rifle can do everything perfectly, but some guns can do most things well.
Guns are really defined by their cartridge, so if you want a gun that will do most things, focus on a round that serves many options.
I also recommend to not be tempted to buy too powerful of a cartridge for the job you have.
There’s a time and place for a big thumper like a .50 Beowulf (engine blocks anyone?) and just thinking it’s plain cool is a valid enough reason.
Remember it can be tempting to buy a stout round to show off but you’re going to pay for the extra materials in the round and recoil to your body.
Narrow down why you’re upgrading your AR-15 and you’ll probably find it’s for one of these jobs:
- Home defense
- Hunting
- Competition shooting
- Training
Depending on what your uses are, bigger doesn’t always mean better.
Availability & Cost
If you buy a gun you have to feed it.
And the cost of ammo is one of the single biggest factors of how often you shoot. Not sure where to buy, see our favorite places to buy online.
When the cost of ammo goes up or you just can’t find it, you won’t be able to shoot. So, definitely factor that in!
Also, the cost should include the necessary modifications you need to make the gun run right.
It may be tempting to build one yourself but remember that these can be finicky. If the upper you build doesn’t run right you’re out of luck.
But don’t worry, we’ll recommend some solid uppers for each new caliber.
Best AR-15 Alternative Cartridges
.300 AAC Blackout (.300 BLK)
The .300 BLK was born out of necessity as a replacement for the sub-machine gun MP5SD which shot 9mm. It needed to be based on the M4 rifle, match or exceed a subsonic 9mm bullet, and be as quiet as possible.
Advanced Armament Company (AAC) took a .223 case, blew the mouth out to .30 caliber, and filled it with pistol powders.
BAM!
You now have a juiced-up .30 caliber cartridge for your AR-15 that needs only a barrel change. No difference in magazines, lower receivers, or bolt carriers.
Pros & Cons of .300 BLK
Some really awesome things about .300 BLK are its performance out of a short barrel and the ability to shoot subsonic ammo with zero problems.
The .300 BLK was designed around a 9-inch barrel and it gets roughly 95% of its full potential with that barrel. Making it the absolute best cartridge for short-barreled rifles and suppressed guns.
Check out our recommended Aero .300 BLK complete upper receivers.
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Prices accurate at time of writing
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It is an ideal home defense gun with subsonic ammunition because it’s hearing safe if you use a suppressor.
If you’ve never lit off a gun, let alone a long gun, in a confined space I will personally attest that it hurts. A lot.
Choose your ammo carefully though for home defense. Large and heavy rounds like the bigger .300 BLK offerings tend to over-penetrate.
There are a few good options though, so take a look at our [Study] Home Defense Overpenetration: Shotgun, Handgun, Rifle for a LOT more detail.
It isn’t perfect though, the supersonic rounds drop like a rock and the subsonic drop like a…less aerodynamic rock.
For subs, you’re looking at about 100 to 150-yards of max effective range. Supersonic you can push to about 300-yards, but it’s not ideal.
6.5 Grendel
The 6.5 Grendel made its debut at the Blackwater Training Facility in North Carolina in the summer of 2004.
The idea behind it was to neck down the 7.62×39 — the round made for the original AK-47 — to .264 caliber to take advantage of the favorable ballistics of the 6.5mm bullet.
Pros & Cons of 6.5 Grendel
The advantages of the 6.5mm bore are the extremely high ballistic coefficient and high sectional density. These two qualities make this round outperform the 7.62 NATO in both terminal and exterior ballistics.
It shoots flatter, stays supersonic longer, penetrates deeper, and has less recoil than a 7.62 NATO.
This sounds like an infomercial but the numbers are there, making this a great round for hunting and competitive shooting.
As a tactical round for home defense, it’s too expensive, around $0.90 to $1.20 a round. It also offers no advantages within 300-yards.
And it’s often hard to find uppers with under 20-inch barrels.
Issues with the 6.5 Grendel range from the common (15+ round magazines are hard to get) to the really weird (how my Yeet cannon can shoot sub MOA with Hornady black and 4+ MOA with Hornady SST).
Grendel really benefits from hand loads, like a LOT. Finding factory ammo isn’t the hardest in the world, but finding one that your rifle really likes though will almost always take some testing.
If all this doesn’t phase you, check out some 6.5 Grendel Uppers.
6.8 SPC
This round was developed as a long-range option for the M4 for the Army’s marksmanship unit. They needed an exhibition round that would work well with the M4 to shoot in competitions and light field use.
It was put up against the .300 BLK and 6.5 Grendel for replacement of the 5.56.
While it performed admirably at ranges further than 250-yards, there was no practical point for the military using it since engagements were usually less than that.
Pros & Cons of 6.8 SPC
This is a very cool round and it’s calling card is as a short range hunting round that shoots further than the .300 BLK and hits harder than the 5.56.
It’s a .270 caliber bullet right around 115-grain that clocks in around 2,600-feet-per-second.
It’s true that it carries 40% more energy than the 5.56, but the real advantage is the extra penetration and ballistic coefficient that comes with the extra bullet mass and cross-section.
The downside to the 6.8 SPC is the availability of magazines.
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Prices accurate at time of writing
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Standard mil spec mags won’t work, because the feed lips and follower are different to accept the wider case.
Of course, the barrel and bolt have to change but you only need one of each, and they can be bought in a package like this one. Multiple magazines, on the other hand, can be hard to track down.
The other problem — like Betamax vs. VHS, 6.8 SPC kind of lost out to 6.5 Grendel in popularity. Anything 6.8 SPC can do, Grendel does just as well or slightly better.
Really, 6.8 SPC doesn’t offer much different — not enough to really carve out a place in the market.
.458 SOCOM
The best of the big woods thumpers, the .458 SOCOM was developed to have serious close-quarters battle (CQB) stopping power for special operations forces.
The reason this cartridge beats out the other big-bore AR-15 cartridges is because of the short-barreled performance and availability of bullets in .458 diameter.
Pros & Cons of .458 SOCOM
The .458 is a necked down .50 AE (of Desert Eagle fame) case which opens it up to a multitude of .458 bullets. It also uses fast-burning powders and heavy bullets that make it ideal for SBRs and suppressors.
Unlike the .300 BLK whose subsonic rounds are a poor choice for hunting, the .458 throws 350-grain slugs that can be used out to 75-yards for hunting thin-skinned game.
With subsonic ammunition, you get performance on par with a hot-rodded .45 Colt and with supersonic rounds, you get .45-70 glory wrapped in AR-15 clothing.
The .458 SOCOM saw limited use in the middle east for CQB operations because it throws a huge man stopper of a round in a small package.
Radical Firearms makes some great .458 SOCOM uppers.
.50 Beowulf
Coming from the minds that brought the 6.5 Grendel is the .50 Beowulf (which then kicked off the big-bore AR-15 concept).
The origins of this round have been said to lie with the military as a means to stop vehicles at security checkpoints and prevent car bombings.
Pros & Cons of .50 Beowulf
The .50 Beowulf is one of the ultimate “wow” rifles. It kicks like hell on both ends, creating a clap of thunder when your wallet slams empty as you buy the ammunition.
The .50 Beowulf is a decent choice for hunting as it’ll certainly drop anything in North America. Trajectory is a slight concern as is the cost and availability of ammunition.
Ammo options have come a long way in the last few years for the .50 Beowulf, though. But once ammo’s gone, it takes a long while before anyone restocks it.
As a home defense round, it serves no real niche. It’s huge but normally comes with hard and deep penetrating bullets. I guess if you’re worried about being able to clap someone from the other side of the house while firing through every wall in your home — send it.
The key to using this behemoth is to get close and use bullets that’ll reliably open up and dump massive amounts of energy.
Find some great .50 Beowulf Uppers from the original maker, Alexander Arms.
6mm ARC
One of the newest kids on the block for the AR platform, there isn’t a ton of information out about the 6mm ARC yet.
Developed by Hornady for “the Department of Defense” we know that the 6mm ARC was officially adopted by… someone, but no idea who.
The ballistics are impressive though and it’s a very soft round to shoot.
Pros & Cons of 6mm ARC
Ballistics are outstanding! Basically, take 6.5 Grendel and juice it up a little. 6mm ARC is supersonic past 1,000-yards from an AR and that is very cool.
The downsides though are long.
Ammo is unobtainable right now and even pre-pandemic the options were Hornady or…Hornady. It’s taken me three months to get my hands on 200 rounds of 6mm ARC.
It is a reloader’s dream though since 6mm bullets have a HUGE range of options that are amazing.
Building or buying an 6mm ARC rifle right now is pretty tough though, because barrels are also difficult to come by.
While availability of ammo and parts will sort itself out eventually, right now you would be a very early adopter of the cartridge and need to know what that means going into it.
We don’t have a recommended list of barrels or uppers yet, but we will once we get some more time with them.
Pistol Calibers: 9mm, .45 ACP, 10mm
Pistol Caliber Carbines are fun. And cool. No one can change our minds on those facts.
While it might seem odd to just make a pistol bigger, a PCC can be a great option for home defense or training. Even in times like these, 9mm is still a good bit cheaper than 5.56.
When it comes to turning your AR into a PCC you have several options. With magwell and magazine conversions, you can use the same lower as normal but switch out the upper.
Pros & Cons of Pistol Calibers
You have a few options when it comes to what caliber you pick, but by far the most common is 9mm. There are loads of conversion kits. Not to mention it’s easy to get barrels and BCGs. Oh, and bonus, it’s way easier to tune.
9mm is great for training. Sure, the recoil isn’t exactly the same, but weapon handling is, making it a great option for lower-cost training. It’s also not a bad option for home defense.
But if you’re feeling sparky, you can also turn your AR into a .45 ACP, .40 S&W, or 10mm PCC.
Bigger calibers like .40 S&W to 10mm can be used for hunting at shorter ranges. And, let’s be real; they’re just fun. Plus, the options of training and such — but less effective since it’s more expensive.
.22 LR
It’s America’s cartridge…older than Coca-Cola…the cartridge most of us learned to shoot on. And it’s pretty awesome in an AR too.
With dedicated uppers and conversion kits, it’s really easy and fairly cheap to get into .22 LR. You’ll need new magazines, but other than that you can get away with just a BCG conversion if you want.
5.56 barrels don’t have the right twist and aren’t the perfect size for .22 LR, but they are close enough that you can do decently well with a standard 5.56 barrel.
Pros & Cons of .22 LR
.22 LR is perfect for small game, teaching kids, plinking fun, training, and a lot more.
Conversions like the CMMG kit are easy to install and inexpensive, and that is on top of .22 LR being 1/5th or less the cost of 5.56.
Downside is that it’s not a viable self-defense round. Even the best .22 LR is still not dead on reliable enough to bet your life on. .22 LR just lacks any kind of punch behind the round.
The other thing to keep in mind is that not all triggers play well with BCG conversions like the CMMG kit. A standard AR has a free-floating firing pin, but most .22 LR ARs or AR kits use a spring-loaded firing pin.
Some aftermarket triggers, especially ones with lower pull weights, don’t have enough punch to reliably run those BCGs. Standard milspec is good to go though!
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Prices accurate at time of writing
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7.62x39mm
The classic Russian cartridge, for many years 7.62×39 ARs got a really bad rep due to reliability issues.
Thankfully, most of those have been solved now and there are some solid options on the market.
Think of it as .300 BLK but cheaper and a little more annoying to get running well in your AR. Once you do get it up and running, though, it’s basically the same performance and advantages.
Suppressor use, short range, need more punch, all of it applies to 7.62×39 like it does .300 BLK.
Pros & Cons of 7.62×39
Remember the reliability issues I mentioned? Ya, those are the biggest cons — feeding and bolt breaking, to be specific.
Feeding issues can be solved by getting a good barrel and using good magazines. We like DuraMag and ProMag for 7.62×39.
Another problem lies in the bolts. These bolts, even great ones, are fundamentally weaker than most other AR bolts. Because of the cartridge size, a 7.62×39 bolt face doesn’t leave much meat on the bone for durability.
LMT, Windham Weaponry, and Young Manufacturing all make great bolts; but you might want to get an extra, just in case.
If you’re really crushing on a 7.62×39 AR platform, though, consider a dedicated rifle. Sure, that knocks it out of “best alternative cartridges” but it will dramatically increase reliability and durability.
Personally, I love the KS-47 from PSA — and it takes AK mags!
The Bad and The Ugly
There are some more caliber conversions for the AR platform that are worth mentioning, but we don’t recommend them. Still, it’s fun to talk about.
5.7x28mm
Yep, it’s the same little guy in the Five-seveN and P90.
For a long time, this round wasn’t available. (The company that made the uppers went belly up.) However, recently CMMG brought the 5.7×28 cartridge back to the AR-15!
The downside is that uppers are expensive, very hard to find in stock, and use several proprietary parts. Let’s not forget magazines are pricey and the ammo itself is a wallet buster!
Basically, the price hurts at every step. It is also kind of a novelty cartridge in the AR. There really isn’t anything it does in an AR that isn’t done as well or better by other rounds for a lot less money.
Now if those OG uppers with the P90 top-loading magazines that dropped spent brass into gutted-out AR mags return…we’ll be all over that!
.224 Valkyrie
We’ve talked a lot about .224 Valkyrie and, personally, I enjoyed it. But as the last few years have rolled out…the Valkyrie is dead in the water…for the most part.
Decent at long range and hunting, .224 Valk had a lot of promise. But issues with barrels, twist rate, powder, factory ammo, and the fact that 6mm Grendel, 6.5mm Grendel, and now 6mm ARC are better in almost every possible way — well, the .224 Valk just didn’t keep up.
It isn’t a bad round and there are still a lot of parts out there, but if you want long-range and hunting…you can do better.
.22 Nosler
Another big splash that later fizzled, the .22 Nosler has also fallen by the wayside much like the Valkyrie.
Designed to be a screamer, this cartridge could push a 70-grain round at 3,000-feet-per-second. Honestly, Nosler is great for pushing a ton of speed out of a small cartridge.
But, as happens with many new cartridges, the factory ammo offerings just aren’t enough to support it. Most of the ammo comes from Nosler but even they don’t produce enough of it, especially right now.
Other brands have almost totally ignored it despite it being a SAAMI spec round.
And, again, with 6.5 Grendel and 6mm ARC on the market, there are simply better options available.
.458 HAM’R
We love Wilson Combat, but the .458 HAM’R is another dead cartridge.
Designed by Wilson Combat for hunting, the specs are basically .458 SOCOM but juiced up — very attractive to hunters!
Sadly, .458 HAM’R isn’t SAAMI approved making this a wildcat of a cartridge. For now, that means Wilson Combat is the only source for parts and ammo.
Of course, that makes things expensive and very limited in selection.
However, Wilson Combat’s 300 HAM’R is SAAMI approved. As the name suggests, it’s a .30 caliber round that is kind of like 300 BLK but juiced-up. More speed, more energy, and flatter shooting make the 300 HAM’R a cool option.
We’ll wait on judging it until some more manufactures start to offer options, though.
Conclusion
Choosing an alternative AR-15 cartridge is fun! But you do need to choose wisely and balance your options.
The hardest part can be just taking the plunge and picking a cartridge (and realizing you might need to learn how to reload that expensive ammo).
Some rounds are still boutique and may disappear in the future but for now, they’re fantastic if the purpose suits your mission.
Choose the one you like best and shoot it until the barrel burns out.
In the meantime, which round do you think will be next for mass acceptance? Let us know in the comments! Ready to trick out your AR-15, check out our definitive list of upgrades or shop for a new AR altogether with our list of the Best AR-15s.
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I have built .556, 6.5G and .458socom from 80% lowers.
I love them all. But for different reasons.
The .458$ is so dope to shoot. It's like holding a grenade and surviving.
The 6.5G is so smooth and has about the same recoil as 556 but the target impact is very noticeably harder.
5.56 is like your mom's underwear, it doesn't stink pretty and everyone has handled it at some point. Bo-ring but good for newbies.
Sad that this drivel is what passes for gun writing these days. This article and website are a joke.
While it may take even longer for the writers to correct the horrible misinformation they've included on the origins of the cartridges, the focus remains: you don't pick the brand or the type of cool looking gun, you specify exactly what you want the bullet to do in terms of range and it's amount of power sent downrange. .223 might not be a great choice on elk and .458 SOCOM a bit overmuch for squirrel - yet too many new buyers are actually getting a membership card in a cartridge thinking how cool it is rather than can it do the job?
That is where most of the disappointment comes from. It's a mismatch from the beginning rather than a selection to fit the task. Be aware the sales hype writers are not going to deliberately deselect themselves from the race by mentioning what the round won't do well and "maybe you'd be better off if you chose that other round."
Range and type of target in specific numbers is the better answer. The 5.56 from a 20" barrel is still a great defensive round - in the terms of combat power - but cutting that barrel down to 14.5 was not the better choice for Infantry - it made it the modern M2 Carbine of this era.
Hence the search for more power, starting with the .458 Socom, which has limited range, and then the 6.8SPC, which was a swing to the other side with good range and more power. But its still not a .308 and in some eyes that made it insufficient - yet the problem there was once again, what was the range and power delivery needed?
Apparently there isn't even much agreement in the service - because both sides were attempting to force a "one gun that rules them all" solution. Nobody in the civilian market has ever attempted that answer and it would be unprofitable to try.
Fit the cartridge to the job and the disappointments dont crop up. Don't be the guy with a Chevette trying to haul a pallet of sheetrock home when you really needed a pickup, don't get a two ton for everything when a 1/2 ton will do most of it.
Range, and target.
"The other problem — like Betamax vs. VHS, 6.8 SPC kind of lost out to 6.5 Grendel in popularity. Anything 6.8 SPC can do, Grendel does just as well or slightly better."
We are not to speak of Betamax anymore. It was the complete opposite and did everything better than VHS; Betamax should have been the Grendel. Sony didn't allow competition in Betamax manufacturing, leading to higher costs for the consumer, while JVC allowed VHS to be made by competing firms thus lowering costs by increasing supply. If you had lived in Europe back then, you likely would have had a Betamax if you could afford to either. In the US it was the opposite and you would only buy VHS even if you could afford both. - Sorry, it's been 20 years since I've heard the word betamax and I'm still triggered at Sony about it - I'll return to my cave now. - Thank you for the great article!
Love my .50 Beowulf - but you have to find rounds that expand at the range you're using them at. I've seen 4 exit holes in whitetail that were the same size as the .50 cal entrance hole, and left no blood at all. Deer ran between 25-100yds with double lung shots(the one that ran 25yds was coincidentally 25yds away, the ones that ran further were all 50 yds away, at my feeder), but one ran 75yds with a heart shot. Just punched a hole through them all, didn't dump any energy. Walked in the direction the deer ran off, and was lucky to find them with 0 blood trail. This year, my .270 winchester model 70 took deer down where they stood at 50yds. 130gr federal bullet, though I prefer Rem Core Lokt. With that .50, bullet type is key.
Well after reading this article sounds like, for me at least, besides 5.56mm and 300 AAC, there not really any good reason to go with any other AR caliber. Maybe 22 lr for cheap training but still an AR in 22 has no appeal to me. Thanks for all the info! Great article.
I love my .458 SOCOM. It’s a mighty thumper, but not so bad tha you want to put it down after a few shots. My 17 and 12 year old daughters have no issue firing it.
What about .223 Wylde?
There is no such cartridge as a .223 Wylde. It is a barrel chambering that allows you to shoot 5.56 or .223. It is a market driven construct that is unnecessary. Just buy a 5.56 barrel and it will do the same thing.
I wonder where.350 Legend and .450 Bushmaster fit in the list.
I happen to have selected the .450 Bushmaster for thumper duty in my lineup. NM mule deer, javelina, and feral hogs here 250 yards and under in a quick handling AR15 with a good red dot optic is sweet. At the time the .50 Beowulf, .458 socom, and .450 Bushmaster were the available and alive thumper rounds I had to choose from. I went with the .450 due to its terminal ballistics with available factory loads. It was a tough choice and Im happy with the results so far. A 250lb hog at 130 yards, and a 213 pound hog at 125 yards shot an 8 count apart at a drinker. Both were DRT. I could not have done that as quickly with my Winchester 88 .308 with factory irons. Pick one you like and find loads that do the job correctly. Figure out the ranges the wep is effective in and go hunting. Projectile choice is key with the big thumpers. As with other ARs we are only a mag slap away from a different load as the situation demands it.
Cheers
Was hoping to hear your take on 350 legend. Unfortunately, for some reason, it was not mentioned.
What about .223 Wylde?
It isn't a cartridge. It is a chambering - you use the same 5.56/.223 as any other AR. So it isn't and alternative either.
I have a 6.5 Grendel upper from Precision Firearms and it is fantastic. Great soft shooter and very accurate. They have a plethora of uppers for your AR in 6.5 Grendel as well as other calibers. Also lots of mags and ammo. I put the upper on a lower I built and couldn't be happier. Check them out. I am a satisfied customer, not an employee. They are always willing to answer questions.
As for opinions on what is most likely to end up massively popular next, if the Army actually adopts something from the NGSW program everyone will want that round. Sig has already released civilian versions of theirs in .277 Fury with intent to release a civilian version of their rifle by the end of next year. If one of the other 2 competitors wins demand for that rifle and cartridge will spike hard. If, like most Army trials, they don't actually buy anything then it will be some time before something else rivals 9mm or .308 or 5.56 for popularity, though 6.5 Creedmoor is making progress.
Take it from a Marine who has used both 5.56 and .308 in Vietnam. You want the 308. You need the 308! You don't want to waste your time with a bunch of "poodle shooter" calibers when life and limb are on the line!
Good article, but what about the 450 Bushmaster?
Great article! Thank you again for the info and explanations you provide, and the the topics you choose. Definetly helps me in choosing my next firearms!
First time I felt compelled to chime in. PWS with an 11.85” barrel chambered in 7.62x39 is the best alternative, and I would argue better to suppress, than most 556 (DI) rifles.
Great article. Keep up the good work.
I want an AR in 300 HAM'R. It seems to have the best combination of what I am looking for. Except I just do not have the money currently to get the parts AND ammo.
Next up in the timeline was 6.8SPC, a Special Forces project actually financed by the Army. They gave them a few thousand, the AMU in Benning worked out the cartridge to fit the demands - at least 50% more footpounds of force downrange from the M4 and it's 14.5" barrel. Nothing about it was intended to be "long range", what they wanted was more power since the 5.56 was said to be emasculated from losing 5.5" of barrel. It would have worked out IF Remington had done their job releasing a valid blueprint spec - but it was flawed, and SPC II was developed to fix it. However, the damage was done, and strangely just in time for AAC - owned by Remington's bosses - to release .300 BO, which was a redrawn .300 Whisper to get around some attribution.
Somewhere in all that 6.5 G was being developed out on the West Coast using the AK derived 6mm cases for long distance precision shooting, and it did earn championship trophies. It usually appeared in longer barrels than SPC because neither cartridge was ever intended for the same purpose. However, AR15 owners quickly conflated them as being the "same" and the internet discussions began to escalate, with 6.8 owners posting pics of trophy kills and 6.5 users plastering charts and graphs galore to make the point it was better than .308. It's not - the idea that a faster smaller lighter bullet can convey the same amount of power further downrange isn't supported by real ballistic application. What it can do is remain stable longer due to a more aerodynamic bullet shape allowing it to remain in the air further with less dispersion and less drop. Again - 6.5 and 6.8 were never meant for the same job.
6.8 magazines were available thru the last panics, Ive bought them and still have a stack. 6.5 mags have the unenviable task of trying to feed a case which demands a curved magazine thru the straight mag well of the AR, which is why the AK mag variants have always done better. But - not compatible. Strangely enough, .458 S is compatible with AR magazines, it was the requirement to get consideration from the Army and done right no modification are needed. .300 BO however does has slight issues with issue mags as the fatter bullets contact the forward ribs that clear 5.56 and there are now .300 specific mags to address it. The more difficult issue now is the ATF making form 4999 in an attempt to outlaw pistols, which may impact the .300 BO more than any as the 9" barrel is the best length - not 16". Strangely, the Socoms have the same issue - designed for short barrels.
There is a lot more to choosing one over the other, the real guideline is this: What range, what target? How necessary is it to keep the bullet power above 1000 foot pounds for an ethical kill, how far downrange? If you don't really need power - it's a paper shooter - don't go big. If you do, the bigger the base of the bullet, the better, to absorb power and keep game loss to a minimum. This is why .375 Socom may be the bigger winner in future, it puts out power with long range and little holdover to 300m, all in a AR15 sized rifle. However - source your barrel and bolt carefully, as the lesser priced variants don't adhere to specs which cause issues.
What about the .350 Legend? I've been stocking up on ammo & mags & waiting for an AR. I live in Iowa, so I think this straight wall round is perfect for deer, coyote & 2 legged predators. Will find out when I can get a rifle.
I would really love to see an updated version of this article
.300 Blackout started as a 3Gun alternate cartridge long before JDJ picked it up as the Whisper. It was already being tried in the early 80's - the first SOF Invitational in Columbia MO had competitors using it - or trying - in order to work around the requirement for a .30 caliber bullet. The overseers of the match tossed it out as back then only Real Men shot .30 from Battle rifles. The majority of rifles used at the match were M1A1's, FNFAL's, and the rare HK91.
The AR15 eventually was allowed, and just the same as in Service Rifle now dominates the game. It simply shoots more accurately do to less recoil and getting back on target faster - something that .300x45 didn't exactly excel at vs 5.56, and ammo then was only available if you reloaded it. Milsurp was cheaper and nobody saw .300 giving them flatter shooting at distances in competition, so, it quickly died. JDJ then picked it up for suppressed use calling it .300 Whisper. A lot of this history is limited to a few books, sales catalogs, etc because this was pre-internet. No, there aren't any links to it - in fact, links get taken down frequently and what we see is a passing snapshot of time constantly changing.
Case in point, ask your mil buddies about the 1954 Army Pistol Trials. The what? Right, to replace the 1911. Very little on the net and one of those things folks under 50 have no idea existed. Read Nonte's Combat Handguns, it's all laid out. That's a book.
As for the .300 - I was there in Columbia and seeing it tossed to prevent the AR15 from being used in competition was a clear overreach of the rules. Funny how we get stuck on a concept and just a few years later the winds of change blow thru anyway.
As said: If ammo costs are important, you will rarely find anything competitive with 5.56, and most alternates are retail pricing - no bulk surplus. As a 6.8 owner, I'm still waiting for battle packs of surplus to be sold out of stockpiles. Oh well. Next project may be a .375 SOCOM, the flatter and further shooting upgrade for the .458. Better legs at longer distances.
At $2 a round reloading will be a necessity.
It'd be interesting to see an updated version of this, taking into account 1)new barrel lengths available in the current market 2)updated pricing for current market 3)inclusion of 225 Valkyrie
Amen to that
My wife has 2 Ruger Minis one in 7.62 x 39 and the other 6.8 SPC she has killed several deer with a single shot with both of those guns. I prefer the AR10s with a heavy barreled Stag 10 in 6.5 Creedmore and a BCL 102 in 308. Both guns have given me long range single shot kills with minimum recoil. I've seen too many woundings and lost deer with the .556 and believe it doesn't belong in the deer woods. My home defense is a 10 gauge double with 00 Buck. I've only got to be close and no one in their right mind will argue with it.
I agree with the option of a 300 AAC blackout for home defense but you probably should add to the article about all the legal fees that go along with owning a SBR/suppressed subsonic rifle.
I'm looking at the 300 HAM'R as a next build...
i love the 458. i bought the radical arms version which most people prefer the tromix. i have had feeding issues that was quickly solved with a mag change .
This article is over 4 yrs old, much has changed with Ammo selection and AR15 parts available to those who build there own. What I have the hardest time with is finding magazines made for each of the different calibers. Being here in NY our mag release has to be disabled. In order to load the 10 round magazine we have to pull the rear pin and load through the receiver that way. But with the magazine locked in place we can keep all the extras on the gun to make it look as scary as possible.
There's no way that article is -- oh wow it really is 4 years old... Um, ya, we need to update this one. Soon!
Have you checked out GunMag Warehouse? We're in California and get most of our mags through them, great selection on even the weirder calibers.
I'm looking forward to the update. Another website put up a similar review recently.
I thought it might offer more insight but.... They plagiarized your article heavily and added nothing.
I thought you may want to know about it
Thank you for the heads-up!
I have to completely disagree with you about 7.62x39. I think this cartridge is the #1 alternate AR round. I can shoot cheap wolf ammo at $3.59 per box of twenty all day through my AR. HUNDREDS of rounds. I run C- products mags and have never had one hiccup. You do NOT need a special lower. Any mil-spec lower works fine. All you need is a bolt, mags and a barrel. 300 black ? $9.00 a box is about the cheapest I can find. That’s not too bad, but if you shoot a lot say 2000 rounds, that’s $500 in savings. Also .300 black isn’t as powerful as 7.62x39. Also,you can find 7.62x39 ammo anywhere. There are more bullet options for .300 blk and, it is superior for shooting subsonic, but that’s about the only advantages I can think of. I’ll take the old Russian round any day of the week over all these other cartridges.
Finally, someone who agrees with my opinion of the 7.62 x 39. When prices of ammo were skyrocketing in the middle of the toilet paper apocalypse, 7.62 x 39 was still available EVERYWHERE and not marked up to scalper prices. The AR15 platform has proven itself to be superior to the AK-47 with more interchangeable parts. The 7.62 x 39 is a no-brainer alternative to the minimal stopping power of the 5.56 and the overpriced, short range 300 blk.
Everyone is entitled to their own opinions, but 6.5 Grendel is an easy choice for me. Pretty much all the information in this article is incorrect in regards to our lord and savior 6.5 Grendel.
Grendel has come a long way in the years since this article was posted, we're updating it soon!
A 50 Beowulf in a home defense application is going to "...pass through...imparting little damage..." Seriously? It's a .50 caliber bullet traveling 1,800 fps! Yes, it will be devastating if it expands, but it's already as large as a lot of EXPANDED 9mm rounds; and I would think is comparable to .45-70 which has been taking down big game with low-tech bullets for decades. But yes, agreed, NOT a great choice for home defense (can you you say "overpenetration"?). And the .300 Blackout is discussed mostly in terms of sub-sonic rounds. Through a short barrel, suppressed, the high velocity Blackout rounds (110 gr, etc.) are very efficient and would be devastating, right? I disagree that the 6.5 Grendel offers no advantage inside of 300 yards. It has advantages in Terminal ballistics progressively getting better at 100, 200, 250 yards over both the 5.56 and 6.8 SPC - all of which are already marginal calibers for deer, for instance, so the advantages of 6.5 G are significant. And of course, no fault of the author, since this article was written, many 6.5 Grendel options have come out. This article needs some work. Very misleading.
This article has so much wrong with it. Grendel bolts for $300? Ha
The Grendel is a barrel burner? Nope, too slow.
This should be taken down or drastically overhauled.
"Velocity is a great thing but without an adequately heavy bullet, velocity is irrelevant. Bullet weight is what causes penetration and lethality.
Cartridges that throw heavy bullets at medium velocities are more powerful than a lighter bullet traveling faster because light bullets lack the ability to penetrate and cause damage."
Irrelevant? Lighter bullets lack the ability . . . ? Really, McKinley? Saying that, that way, unqualified, given the long-standing well known raging debate about velocity vs weight, is . . . I''ll be kind, you should be embarrassed. Very embarrassed.
Cross section, sectional density, these things have nothing to do with penetration? But especially velocity - which is squared in the formula for energy, a fact which I know you "big bullet" devotees hate - has A LOT to do with terminal ballistics. Plain and simple, more energy spent = more damage done. Just physics.
I understand the tendency to favor weight, which you can feel, and size, which you can see, over velocity, which you can't feel or see, and which to a simple mind is just a mathematical construct. You prefer weight over velocity, fine. Never mind the math. But you go waaaaaay too far.
Would you rather be hit by a two ton truck going 2 mph or a 1/2 pound rock going 2,500fps? A thrown brick or a 55g bullet at 2,700fps?
Glad someone said it. If you want penetration, you need speed. The axiom "velocity beats armor" isn't just a fantasy. A shotgun slug, though far heavier, will never penetrate a plate, while a 62gr steel core penetrator in measly 5.56 will tear the wearer a new breathing hole without blinking at the armor.
I feel like this article is due for an update and correction of some of its content.
It's actually currently in the process of a major update!
Completely disagree on the 7.62x39. Author doesn't seem to be an "expert". The advantage the 300 BLK has over the 7.62x39 is of course the use of the same bolt and magazine. The 300 BLK has no ballistic advantage over the 7.62x39 and is far less available and far more expensive. A thousand rounds into it and you have paid for the bolt and magazines needed for 7.62x39. And enough with the "subsonic" and "suppressors". You're not an "operator".
Absolutely
I own a .458 socom,2 6.8 spc’s, 3 300 BLK(one is an SBR) and a 6.5G. I reload for each caliber and can speak for each ones pros and cons first hand. Here’s what I’ve learned:
-458 socom; best big bore for reloading due to the case design. Headspaces on the shoulder. Better feeding and uses many 5.56 mags including GI(lancer works best) Best SBR performance in big bore AR’s. Great bullet selection with weights from 140-600 grains. Excellent hunting caliber for <200 yards. I’m loading 225gr to 2,200 fps and 300 gr to 1900 fps from a 18” barrel 1:14. Cons; expensive, poor trajectory, low mag capacity, not ideal for home defense.
-6.8 SPC; say what you will but this is in my opinion the most well rounded caliber for the AR 15. There’s calibers that will outperform it in every category but but none can say they do it all “well” like the 6.8 can. Accuracy is sub MOA. Recoil is negligible. Works very well in SBR format. Great medium range ballistics. Bullets selection is great. I’ve loaded every bullet from 85-130 grains and settled on the 95 gr Barnes TTSX as my go to for dropping game. My chrono reads 2875 fps from my 16” barrel with the 95 gr pill. Not too shabby. I can make one hole at 100 yards with a 5 shot string from a rest.
Cons; somewhat expensive ammo if you don’t reload. Range limited to <500 yards with most loadings with a few pushing past 800 staying super(Berger).
-300 BLK; My first build was a purpose built subsonic suppressed SBR. It has an 8.5” 1:7 barrel and a Silencerco Omega under a 13” hand guard. I’ve built this gun to cycle with pistol powder like enforcer. It’s very quiet and very accurate. I’m pushing 240 gr pills at just over 1000 fps. There’s plenty of expanding sub bullets available for this caliber so hunting with subs is very doable within the calibers respective range. Great short barrel performance especially for subs. Only need a barrel swap to convert. My other 300’s are built for super or subs. The super performance is nothing special but the flexibility of the cartridge is amazing. You get 7.62x39 like performance with supers and crazy quiet high BC performance with subs that outshines any pistol caliber carbine. My opinion is this caliber is best in it’s subsonic form. It’s supersonic loadings are surpassed by many other caliber options. My other 300 is a bolt action so I’m not going to discuss it here.
Cons; supersonic performance is subpar. Subsonic weight bullets are expensive.
-6.5 Grendel; I bought an upper off a friend chambered in 6.5 G. I started experimenting with different powders and bullets and came to the conclusion that this caliber doesn’t do anything that the 6.8 can’t do except use bullets that have less drag. Even with an extra 4” of barrel I can only get a 100 gr bullet to 2650 fps. My 16” 6.8 can push 95 gr bullet to 2875. Sure the higher BC means it stays super longer, but who’s really taking shots past 400 yards on living targets. For punching paper at long range it’s an admirable choice, but the 6.8 little brother is better at that(Valkyrie). You can use a 16” barrel for this caliber, but it really needs at least 20” to reach its full potential whereas the 6.8 only needs 16” and works well at 12”. It’s fun to shoot and extremely accurate, but I’m just not sure where it belongs. It scores high in long range accuracy, but that’s about it. You can SBR it, but the caliber gets anemic when you get shorter than 14”. Still a better choice than 5.56 any day and holds its own with the 6.8. I’m just not impressed with its practicality. I hunt, and I’m not risking a shot past 400 yards with any caliber for fear of not making an ethical kill. So in my situation it’s a caliber that rarely sees anything except the range.
The only cartridges in serious consideration are 6.8 and Grendel and both have
shortcomings.They both lack case capacity to be flexible enough and bullet selection
that would be limiting on future improvements.
6.8 improves terminal performance dramatically via bullet weight and diameter but
short,fat bullets have poor ballistics,poor penetration and run out of range quickly.
6.5 Grendel addresses some of those but it doesn't get into the range of bullets
best for caliber.Apparently feeding problems is another issue with Grendel.
According to the research and number crunching I have done for two years
ideal bullets for SPC case would be 117 to 120 grains in .257.This would improve
it's shotcomings.Penetration,ballistics and range.Otherwise case is very long and
maxed out on lenght which limits its bullets to short,fat type 1" to 1.1 " long.
Grendel has to much bullet setback into the case intruding case cap.with
longer bullets and raising internal pressure.Please look at crossection pictures
of both.
Curious as to what your opinion is on the .450 Bushmaster?
Glad to see someone else raise .450 Bushmaster for discussion.
Love mine, doesn't kick as hard as my .270 Win. Quite accurate at 100 yds.
A shame so many authors go for the .458 SOCOM because of a greater selection of projectiles. These are heavy hitting high bullet weight rounds, you don't need 20 different weights and styles (HP, FMJ, etc.). Some 250 grs, some 300 grs (HP) and some 395 grs hard cast Buffalo Bores, and you've covered most uses for the round. Black Butterfly ammo makes a nice range of custom rounds for the .450 BM.
My same thoughts
When did the grendel become a barrel burning monster? Do your homework. 2500-2600 fps is not even close to being a hot rod. Granted this article is 2 years old, but the data has been around for many years previous. Bolts for 300 dollars is also a bit off base. Sure, for top end absolutley for a complete bcg.. Same goes for 5.56, 6.8 spc, 300 blk, etc. Better research will make for better reporting. Sorry to disappoint, but the grendel is sticking around for years to come.
Overbore would suggest Grendel barrels will last longer than both 5.56 and .308
300 blk. Supersonic. Period.
Two years later looks like these guys just coppied and pasted your article, same typos and all, lol. gunnewsdaily.com/best-ar-15-calibers-cartridges
Hi Chris, thanks for letting me know. I know we were *inspiring* in many aspects for them...but this takes the cake.
We fail to mention the cheap russian 7.62x39 ammo as well as cheap russian 6.5 grendel ammo. The russian 7.62x39 ammo shoots sub moa in my 7.62 AR. It sure is better than .50/round for 300blk.
224 Valkyrie the baddest kid on the AR15 block!
Been hearing a lot about it...looking forward to testing it out.
The 6mm AR (6mm Grendel) improves on the capability of the small Grendel cartridge case.
Ballistics of the 6.2 mm (243 bullet) shot from the Grendel case gives you a cartridge that the 1300 yrd F class shooters say is the best round they have found for shooting out of an AR15 platform. Go to 6mmAR.com. The future of the Military combat rifle is the 6mm (243), or the 6.5mm Cartridge.
Thought this was a 7 year old article. Clearly no research or parts search for 6.5 grendel. Parts are a plenty and pretty much the same price as as 556
Well, a year after you wrote this I now own an 18 and 16 inch Grendel. Silly me, huh? I did it because I like my 6.5 creedmoor rifle so much that 6.5 in an AR seems attractive. Especially when it can do much of what my AR10 does but lighter and with much less recoil. Since the bore is bigger and the pressure less than a 5.56 I don't see it as as barrel burner but if it is some day then an $80 barrel will replace it. Both run like a Swiss watch and are easy to shoot. I thiink it is goiing to be a very popular hunting round where 223 is outlawed and 300 blk runs out of gas. Thinking about a 14.5 inch pistol next.
Do you feel like you lose much switching from the 18" to 16" barrel 6.5g ?
Uhhh..... You got a few things wrong here bub. Faster rounds WILL penetrate better than heavier slower rounds. And you're wrong about the 6.5 Grendel's "Debut"......
At the end of the article the three rounds to avoid in an ar-15 5.45, 7.62x39 and 5.56. Does that mean certain types of .223 ammo you wouldn't avoid?
Hi Josh, those three are just the picture. Only two rounds to avoid!
Time to update the article, with the Nosler 22 brass, you can now use the 5.56 reli-a-bolt to run 6.8, and only need the barrel and magazine to convert. Also there is a new kid coming known as the 358 MGP, that will use the 22 Nosler brass as well, although the naming of the cartridge is not yet finalized, and it is still under development, it is yet another good choice coming down the pipe. I would also consider the 22 Nosler brass to be a good replacement for 5.56 brass to shoot the .30 cal bullets, the extra powder capacity would bump up the performance, if only a brave soul would bring it to life, and Nosler would kick the production up on the brass, we would all be in hand loader heaven.
So much wrong about the Grendel.
No, 6.5 Grendel is NOT a barrel burner cartridge. Pressures and velocities are moderate. Barrel life is quite good.
No, Grendel uppers and barrels under 20" are NOT hard to find. 16 and 18 are both very common.
No, Grendel bolts are NOT hard to find and they cost around $75.
No, Grendel ammo is not rare or expensive. Steel case Grendel ammo costs less than 0.25 a round. Even match grade Hornady costs less than $1 a round.
The standard 25 round ASC magazine looks like any other metal AR mag.
I entirely agree. I've got a 16" Grendel barrel with 2 bolts and 10 ASC mags and the the whole thing cost about than $400.
I prefer AMAX to the steel stuff, which is no more expensive than .223 if you reload.... Which is to say, cheap.
And it's nothing to reach out to 600 yards easily. The rifle's good for more. I've got to find more land.
Oh, and my barrel's fine, by the way. What a hatchet job on the Grendel (see: "It offers no advantages for you within 300 yards" as if a .264 supersonic wouldn't offer slightly better penetration and terminal ballistics than a .223) but there's an obvious bias towards 6.8 and the truth is the Grendel makes it look bad.
Yea...I was lost when he wrote that...several of his points were off...most were off
A grendel bolt is hard to find and $300? Do you even do any research?
My bolt came from Midway and costs less than $100. Took maybe 10 minutes to find and buy..
Well...I believe the young fellow is talented but he obviously leans in his preferences. There is a bit of a problem for me in the comparison of apples vs oranges when it came down to the Grendel. I have several AR type rifles that shoot 4 different calibers. If you are going to speak of effective ranges, lets be sure and mention barrel length. As a for instance, I have a 24" barrel on my Grendel that I've recorded shooting a 123 gr. Hornady SST @2650 fps and with a BC of .510, it is still supersonic at 1200 yards...As far as the Grendel dying...no, I'm pretty sure it won't. Especially since the current 6.5/264 craze that was started with the 260 Remington and given an incredible shove with the popularity of the Creedmore. Nosler even came out with its 6.5 screamer the 26 Nosler.
I think you should add the new kid on the block, the 25-45 Sharps. I'd like to see how you weigh in the PRO's. Since there are no con's this should be easy!
I'm with you on this caliber, Troy. I'd love to see the 25-45 in the mix. I'd also like to see a comprehensive comparison on all standard AR-15 caliber conversions, including bullet weight range, velocities, terminal ballistics, effective range, etc.
I personally shoot (aside from the .556) the 300BLK and love the cartridge. Outstanding hunting rifle, with the 100 and 125gr bullets, for deer, here in Cajun country.
I really enjoy the website especially since it sometimes includes a CA perspective. It might be helpful to add the .223 and 5.56 in your ballistic comparison table.
Hi Dave, thanks so much and great idea when we update the article!
i dont quite understand why youll left out the best of all, the ,308. its the pick of nato and many militarys and there is a very wide selection of ars. you guys make no sense whatsover
Hi Joe, we didn't leave it out! Just consider it a different animal as the AR-10. Articles on that coming out soon!