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Best Alternative AR-15 Cartridges and Calibers

It’s cool right now to rag on the 5.56x45mm cartridge.  

Maybe it’s because most people just want something new and don’t necessarily “need” a new one.  Which I sure do understand!

If you feel like you need a bigger caliber, there’s a lot of useful options and a recent flood of gimmicks that have come out.  It’s getting hard to tell the two groups apart.  

But don’t worry…

We’ll go over few of the best AR-15 cartridges and calibers that offer more oomph than the standard 5.56 NATO, along with all their positives & negatives:

  • .300 Blackout
  • 6.5 Grendel
  • 6.8 SPC
  • .458 SOCOM
  • .50 Beowulf
Common Rifle Calibers
Common Rifle Calibers

Table of Contents


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.  

Although the most common upgrades, .300 BLK, 6.5 Grendel, 6.8SPC, and the big boys .458 SOCOM and .50 Beowulf are all cooler and more powerful than the 5.56.

Picking the right rifle cartridge can have real-world consequences that affect lives and can make you look like an idiot at the range (and your bank account) if you don’t pick the right one for your purpose.

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 of power are the same thing, and while they are related…they are two different beasts.

Defining the exact killing 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.  

Moar Power
Moar Power

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 and depending on what you’re shooting at you may need far less than you think.

Flexibility Fetish

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 one rifle can do everything well, but some guns can do most things well.

Gun are really defined by their cartridge, so if you want a gun that will do most things, focus on a round that serves well.  Also keep in mind that with the AR-15 you can usually get a new cartridge or caliber with a new upper and magazines!  

You just can’t get more flexible than that!

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

For all three of these remember that bigger than the 5.56 means better than the 5.56.  How big you need to go is determined by the job you have in mind.

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 place to buy online.

Feed Your Rifle
Feed Your Rifle

The cost also has to include the necessary modifications you need to make the gun run right.  It may be tempting to build one yourself but remember that these rounds 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.

When the cost of ammo goes up or you just can’t find it you won’t be able to shoot.  The only cartridge here that is really common is .300 BLK with 6.8 SPC coming in at a close second.

Consider how you’re going to find ammo during a scare a high demand can be just as bad as a low supply.  Really consider this because shipping ammo can be banned at any moment.  Just ask California, it can be a fight to fix once it happens, remember to be vigilant and ready to resist attempts to take away your rights.


NONE, of these cartridges are ever going to supplant the 5.56 as the standard for NATO or police forces causing the prices of these cartridges to drop.  Yes, the costs of these rounds have come down but there is trillions of dollars worldwide behind the 5.56 and no amount of improvements are going to change its use worldwide.

Still Loved by the Professionals
Still Loved by the Professionals

Sneak Peek

CartridgeCost Per roundChanges to rifleUses
.300blk$$BarrelHome defense, hunting, target shooting
6.8 SPC$$Barrel, Bolt, MagazinesCompetitive shooting, hunting
6.5 Grendel$$$Barrel, Bolt, MagazinesCompetitive shooting, hunting
.458 SOCOM$$$$Barrel & BoltHunting
.50 Beowulf$$$$Barrel & BoltHunting

Ballistic Comparison

CartridgeVelocity*Energy**Drop at 300 yards***Effective Range
.300blk125gr @ 2200fps1300ft-lbs-25”350 yards
6.8 SPC110gr @ 2500fps1500ft-lbs-19”450 yards
6.5 Grendel120gr @ 2450fps1600ft-lbs-18”450 yards
.458 SOCOM300gr @ 1800fps2100ft-lbs-53”200 yards
.50 Beowulf400gr @ 1800fps****2878ft-lbs****-50”200 yards
  • *Max loading from Nosler Reloading manual
  • **At muzzle
  • ***Sighted dead on at 100 yards
  • ****According to Alexander Arms


.300 AAC Blackout (.300 BLK)

L to R: 125gr .300 BLK, 150gr .300 BLK, 220gr .300 BLK, 5.56, 7.62x39
L to R: 125gr .300 BLK, 150gr .300 BLK, 220gr .300 BLK, 5.56, 7.62×39

The .300 BLK was born out of the necessity to have a replacement for the sub-machine gun MP5SD which shot the pistol 9mm.  It needed to be based on the M4 rifle, it needed to match or exceed a subsonic 9mm bullet, and it needed to 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.


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.

It is currently the only semi-auto cartridge that will reliable feed both supersonic and subsonic ammunition without hiccups.

Pros & Cons of .330 BLK

The really awesome things about .300 BLK is 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.

Aero Precision 10-in .330 BLK Uppers
Aero Precision 10-in .330 BLK Uppers

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 you WILL have hearing damage!

The problems with over penetration of the .300 BLK subsonic rounds take a back seat to the guaranteed hearing loss that will come out of a confined space shooting.

It isn’t perfect though, the suppressed rounds aren’t effective past 75 yards and none of the rounds have much steam after 250 yards.  This is really a 300-yard maximum gun, mostly because of the excessive drop that occurs after you get past three football fields.

Readers' Ratings

4.94/5 (566)

Your Rating?

6.5 Grendel

L to R: 7.62x51, 6.5 Grendel, 5.56
L to R: 7.62×51, 6.5 Grendel, 5.56

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 the extremely high sectional density.  These two qualities make this round out perform 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.  This round performs best for hunting and competitive shooting.

As a tactical round for home defense it’s too expensive, around $.90-1.20 a round.  It also offers no advantages within 300 yards.  And it’s hard to find uppers with under 20″ barrels.

The main downsides of this round is the high barrel erosion, high cost of ammunition, and difficulty finding magazines.  Even basic parts like bolts and barrels are expensive.  A Grendel bolt can run you over $300.

The weird magazines are banana shaped like an AK’s, which isn’t inherently bad, it’s just awkward with an AR-15 lower receiver.  The 6.5mm bore burns out quickly but this isn’t normally a problem because the ammo is rare and usually expensive.

If all this doesn’t phase you…check out some 6.5 Grendel Uppers.

6.8 SPC

5.56, .300 BLK, 6.5 Grendel, 6.8 SPC
5.56, .300 BLK, 6.5 Grendel, 6.8 SPC

This round was developed as a long range option in 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.

What we do know is 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

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 115gr that clocks in around 2600fps.  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.

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, while multiple magazines can be hard to track down.

.458 SOCOM

.458 SOCOM vs 5.56
.458 SOCOM vs 5.56

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

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 SBR’s and suppressors.  

Unlike the .300 BLK whose subsonic rounds are a poor choice for hunting, the .458 throws 350gr+ 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 clothes.

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 and can be suppressed easily because of its short barreled performance.

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 for the military to stop vehicles at security checkpoints to prevent car bombings.

5.56 and Two of His .50 Beowulf Big Bros
5.56 and Two of His .50 Beowulf Big Bros

Pros & Cons

The .50 Beowulf is the one of the ultimate “wow” rifles.  It kicks like hell on both ends and it creates 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.  

It’s currently loaded by a few ammunition houses but lacks options with premium bullets for high performance hunting.

So you’ll have to get started reloading.

As a home defense round it serves no real niche.  It’s huge but normally comes with hard & deep penetrating bullets.  That would make this round just as effective as using an M855 5.56 round for home defense in the sense it would pass through the target quickly imparting little damage.

The key to using this behemoth is to get close and use a bullets that’ll reliably open up and dump all of its massive amounts of energy.  The .50 Beowulf is a round that’ll stomp most anything that walks (or drives) in North America and impress all your friend to boot!

Find some great .50 Beowulf Uppers from the original maker, Alexander Arms.

Cartridges to Avoid

We’ve gone through some all-star AR-15 alternative cartridges…what are some to avoid?

Cartridges to Avoid in AR-15
Cartridges to Avoid in AR-15, 7.62×39 and 5.45×39


5.45×39 was Russia’s answer to the 5.56 M16 on the battlefield as the ammo source of the AK-74.  It’s been regarded as black magic death and the reason for maimed soldiers since the late 70’s.

Rounds used by the Mujahadeen in Afghanistan were so lightly constructed that they ricocheted and blew up when they hit wall boards.  The bullets didn’t penetrate well and they didn’t kill well, but they did get a reputation for nasty superficial wounding.  

That’s where the round’s wide wounding and explosive-like myth came from.

The main selling point of this round was that in years past you could find cheap surplus ammo…but the supply has long dried up.  This leaves the steel cased Tula Ammo and Wolf on the market, but using it can have negative implications in direct impingement guns.

I say skip the 5.45 and go back to the regular 5.56.  You don’t gain anything in the AR-15 when you switch the 5.54×39 except a lighter wallet and a less useful weapon.


The real OG of intermediate rounds which fed the infamous AK-47, this was the cartridge that really kicked off the arms race of intermediate carbines.  A true .30 caliber it launches 120gr bullets or so at close to 2200fps from a rifle length barrel.

Seems like a perfect round right?


The taper of this case makes it necessary for dramatically curved magazines and custom lower receivers to work well.  It also mostly uses the steel cased ammunition that uses the polymer coating that doesn’t work the best in direct impingement guns.

The 7.62 doesn’t offer anything the growing .300 BLK does better and doesn’t come in nearly as many loads and isn’t readily suppressed.  Skip this round and get the .300 BLK.

However, if you must…try to get a custom lower receiver (like the RRA) that accepts an AK-47 magazine and moves the pistol grip further back to make it easier to rock the magazine forward.  

RRA LAR-47 Rifle
RRA LAR-47 Rifle


Choosing an alternative AR-15 cartridge is a balance between different sacrifices of power, cost, and availability.

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 (cough, cough…6.5 Grendel…) but for now they’re fantastic rounds if the purpose suits your mission.

It’s hard to read the tea leaves for which round will be the next super star.  Choose the one you like best and shoot it until the barrel burn out.  

In the meantime, which round do you think will be next for mass acceptance?  Or have we persuaded you to just upgrade your 5.56 AR-15.

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52 Leave a Reply

  • Tirod

    .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.

    November 29, 2020 2:17 am
  • Robert L Scott

    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

    October 28, 2020 5:42 pm
  • Sharkey

    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.

    April 12, 2020 10:06 am
  • Zeus

    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.

    April 2, 2020 7:57 am
  • Nolan

    I'm looking at the 300 HAM'R as a next build...

    February 23, 2020 10:16 am
  • don

    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 .

    February 14, 2020 6:21 pm
  • Buck

    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.

    January 27, 2020 2:36 pm
    • David, PPT Editor

      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.

      January 27, 2020 4:08 pm
      • Alex

        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

        February 22, 2020 10:17 pm
        • David, PPT Editor

          Thank you for the heads-up!

          February 23, 2020 6:32 am
  • John

    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.

    December 21, 2019 1:30 pm
  • Cannon Bailey

    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.

    October 27, 2019 9:27 pm
    • David, PPT Editor

      Grendel has come a long way in the years since this article was posted, we're updating it soon!

      October 28, 2019 6:23 am
  • John Shumay

    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.

    September 28, 2019 9:35 am
  • Patrick Mendyka

    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.

    April 4, 2019 6:26 am
  • John Haley

    "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?

    April 3, 2019 4:52 pm
    • Tim

      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.

      September 19, 2019 11:58 pm
  • Dustin

    I feel like this article is due for an update and correction of some of its content.

    March 18, 2019 1:29 am
    • David, PPT Editor

      It's actually currently in the process of a major update!

      March 18, 2019 2:31 am
  • Mark Davis

    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".

    December 22, 2018 7:56 am
    • Daniel Melvin


      March 2, 2019 5:05 pm
  • Ballastically Inclined

    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.

    October 7, 2018 10:41 pm
  • Paul

    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.

    August 20, 2018 11:49 am
  • Michael

    Curious as to what your opinion is on the .450 Bushmaster?

    August 13, 2018 12:53 pm
  • Devin

    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.

    June 14, 2018 9:30 pm
    • William Hobbs

      Overbore would suggest Grendel barrels will last longer than both 5.56 and .308

      February 3, 2019 8:11 am
  • Jason

    300 blk. Supersonic. Period.

    May 21, 2018 4:55 pm
  • Chris

    Two years later looks like these guys just coppied and pasted your article, same typos and all, lol.

    May 15, 2018 6:03 pm
    • Eric Hung

      Hi Chris, thanks for letting me know. I know we were *inspiring* in many aspects for them...but this takes the cake.

      May 16, 2018 1:36 am
  • SC Gunslinger

    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.

    January 2, 2018 6:43 pm
  • Ticklicker

    224 Valkyrie the baddest kid on the AR15 block!

    December 19, 2017 2:29 pm
    • Eric Hung

      Been hearing a lot about it...looking forward to testing it out.

      December 20, 2017 6:01 pm
  • Ticklicker

    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 The future of the Military combat rifle is the 6mm (243), or the 6.5mm Cartridge.

    December 3, 2017 11:25 am
  • rub

    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

    November 29, 2017 7:26 am
  • RON

    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.

    September 12, 2017 5:46 am
    • Rog

      Do you feel like you lose much switching from the 18" to 16" barrel 6.5g ?

      October 24, 2017 12:47 am
  • Tyler Colt

    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"......

    August 11, 2017 4:01 pm
  • Josh

    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?

    July 23, 2017 10:20 pm
    • Eric Hung

      Hi Josh, those three are just the picture. Only two rounds to avoid!

      August 6, 2017 1:56 pm
  • Gerald

    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.

    July 17, 2017 8:26 am
  • Ron J

    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.

    May 12, 2017 9:19 pm
    • Mark

      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.

      August 5, 2017 11:09 am
    • RiverManPaul

      Yea...I was lost when he wrote that...several of his points were off...most were off

      September 26, 2017 12:54 pm
  • Josh

    A grendel bolt is hard to find and $300? Do you even do any research?

    May 4, 2017 5:34 pm
    • RON

      My bolt came from Midway and costs less than $100. Took maybe 10 minutes to find and buy..

      September 12, 2017 5:49 am
  • RiverManPaul

    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, 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.

    February 3, 2017 11:48 am
  • Troy

    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!

    January 23, 2017 4:53 am
    • Jeff

      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.

      June 6, 2017 10:39 am
  • Dave

    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.

    November 3, 2016 1:07 pm
    • ehung

      Hi Dave, thanks so much and great idea when we update the article!

      November 7, 2016 9:44 pm
  • joe allen

    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

    October 22, 2016 5:46 pm
    • ehung

      Hi Joe, we didn't leave it out! Just consider it a different animal as the AR-10. Articles on that coming out soon!

      October 23, 2016 6:15 am
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