Modern Intermediate Calibers 004: The 6.5 Grendel

Two 6.5 Grendel rounds and related cartridges. Left to right: 7.62x39mm, .220 Russian, 6.5 Grendel 123gr SMK, Wolf 100gr FMJ.

Two 6.5 Grendel rounds and related cartridges. Left to right: 7.62x39mm, .220 Russian, 6.5 Grendel 123gr SMK, Wolf 100gr FMJ.

One of the most ballistically interesting intermediate calibers ever developed is the 6.5 Grendel, developed by Arne Brennan with the assistance of Bill Alexander, and promoted heavily by the latter’s company, Alexander Arms. The 6.5 Grendel is interesting because it combines a wide case head based off the 7.62x39mm parent case with a short case length and ample room for long, slender bullets with low drag coefficients. As a result, the 6.5 Grendel is, very unusually for an intermediate caliber, well-designed for retaining energy at long distances.

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The 6.5 Grendel is available with a very wide variety of bullet weights, from 90grs to 139 grains. The variant with the lightest loaded weight is the 100gr steel-cased load from Wolf, which weighs a very modest 14.7 grams (227 grains), while the “flagship” 123gr Sierra MatchKing Grendel load weighs 17.8 grams (275 grains), one of the heaviest rounds we will consider.

Note: All ballistic calculations are done with JBM’s Trajectory calculator, using the ballistic coefficient type appropriate to the projectile being modeled, and assuming an AR-15 as a firing platform. Also, keep in mind that there is no single true velocity for a given round; velocity can vary due to a large number of factors, including ambient temperature and chamber dimensions. Instead, I try to use nominal velocity figures that are representative of the capability of the round in question. In this particular case, gathering firm velocity figures for the 6.5 Grendel was a special challenge. Nominal velocities are only ever roughly correct, but it took more time than normal to arrive at the figures shown here. While I have tried to make them representative, readers should not treat them as gospel.



Nathaniel F

Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. In addition to contributing to The Firearm Blog, he runs 196,800 Revolutions Per Minute, a blog devoted to modern small arms design and theory. He can be reached via email at nathaniel.f@staff.thefirearmblog.com.


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  • xebat

    So what is the best potential replacement for 5.56 for general purpose military applications ?

    6.5 Grendel ? 6.8mm Remington SPC ? .300 Blackout ?

    • BillC

      I replied to you in the wrong spot.

    • None of them, I suspect.

      • Bill Maxwell

        The solution is to use plain old FMJ with the proper twist rate, Im not sure why the laws of physics and the understanding of gyroscopic stability seem to not apply to military rifles……..

      • iksnilol

        What about replacing 7.62×51 with 6.5 grendel? Or with the 6.5 caseless which is even lighter.

        In other words instead of 7.62 and 5.56 have 5.56 and caseless 6.5

        • Nobody is, or for the foreseeable future will be making caseless 6.5mm.

          • iksnilol

            LSAT?

          • Stan Darsh

            Better yet, why not stick 6.5 Grendel 123SMK bullets into the 5.56 Telescoped/Caseless ammo for the LSAT and carbine?

          • wclardy

            Because the telescoped ammo is a solution still in search of a real problem that it would solve?

      • TechnoTriticale

        re: None of them, I suspect.

        Concur. Anything that fits through an AR15/M16/M4 lower (OAL), doesn’t seriously weaken the bolt face, and is compatible with STANAG mag sidewall ribs, is going to be a bundle of compromises (and perhaps introduce interchange hazards with the installed base). Nothing so far in the way of alternate cartridges so far proposed has sufficient advantage over the M855A1 to be worth the trouble.

        Plus we have the on-going distraction of caseless, the ever-present Congressional and DOD politics, and of course budget limitations.

        What would really be needed in the way of a new intermediate military round probably requires a clean slate approach to the entire weapon system, with little assurance that the process would actually result in something optimized for the warfighter’s needs in the next conflicts.

    • DIR911911 .

      7.62×51 . . . end of discusion

      • xebat

        You do know NATOs main service rifle cartridge was 7.62×51 and was too heavy and had 30% less ammo capacity in average for the regular infantryman.

        • 7.62 NATO is more like 50% less in terms of weight; 6.5 Grendel would be about 30% less.

          • ostiariusalpha

            25%

          • 33% less with 123gr brass cased ammo. That figure gets higher when you consider you really should be using steel mags with the Grendel.

          • ostiariusalpha

            My steel mag gets 24 rounds in it, that gives the 5.56 a 25% higher capacity.

          • ostiariusalpha

            The steel mags can’t exactly be ignored, but as far as the ammo, only the 100 gr steel cased Grendel cartridges can really pass as a military round. While you could make a heavier ball round, no one at Alexander Arms has really attempted to do so. Which isn’t surprising, since it wasn’t created as a combat round in the first place.

            Wolf 6.5 Grendel 100 gr – .518 oz
            Federal M193 55 gr – .410 oz
            Federal M855A1 62 gr – .421 oz

            That’s a 26% advantage for the M193, and a 23% advantage for the M855A1.

          • With the lighter Wolf ammo (which doesn’t have nearly as toutable ballistics as the 123gr stuff), you’re looking at something like this:

            5.56
            30 rounds x 11.9 g / rd
            113 g per mag
            = 15.67 g / shot

            6.5
            25 rounds x 14.7 g / rd
            163 g per mag
            = 21.22 g / shot

            So 0.738 Grendel shots per 5.56 shots, or a 26.2% reduction.

    • Blake

      5.45×39 Russian 🙂

      • mechamaster

        with a proper bullet weight, twist rate and barrel lenght too…

    • mechamaster

      Maybe for the “7,62x51mm Replacement / Supplement” topic, it will be easy to answer…

    • The cartridge that is fielded after the 5.56 is likely to be a cased telescopic polymer cartridge, not another brass rifle cartridge.

      • wclardy

        Telescoped rounds make a lot less sense when you factor in the impact on rifle design. Fat rounds require fat receivers, and short, fat rounds require much more careful design for reliable feeding than long, skinny rounds with smoothly curved front ends.

        • The Steyr ACR figured it out in 1987, and incorporated a 2200 rpm hyperburst feature – and that was before computerized design. So I think they can make it work now.

          • wclardy

            They may have produced a rifle/ammunition combination which was competitive during the testing, but there is an open question as to how well that would have carried over into production.
            Remember, the AR15 and M16 displayed no significant issues with extraction until the Army started wide-scale adoption of the M16 and changed the powder use to simplify making the ammunition..

          • I believe not chrome lining the chambers in a tropical jungle war was also an issue.

  • BillC

    No. That topic has already been beaten to death. It isn’t going to happen. Every time anybody brings up a replacement, it’s because they have a weird hardon for XX caliber. No one is saying 5.56mm is perfect, but it’s not being replaced by anything, especially with a cartridge system that is trying to both the roles of 5.56 and 7.62 NATO; especially with the new flavor of M855A1 and heavier 5.56mm.

    • BillC

      That was supposed to be in reply for xebat.

    • noamsaying

      Cartridge selection really boils down to what is the main purpose of your weapon. I am getting a Six8 from LWRC using the 6.8 to hunt hogs, and it is a cartridge with a little more oomph than a 5.56 that my wife can comfortably shoot for home defense. A shotgun is a little much for her and 7.62 NATO is out of the question, plus 7.62 NATO tends to go through more walls. My kids will inherit the gun, and probably wonder why their dad selected such a goofy caliber. 5.56 is great for some uses – and definitely less expensive.

      • BillC

        And there ya go, horses for courses. Proper selection. For a “do-all” 5.56mm is it because the bullets are light (carry more), cartridge case are established (fit more in a mag), and recoil is relatively light (shoot more accurately and faster in terms or recoil management). The effectiveness of 5.56mm on humans and animals is usually blown way out of context in terms of its effectiveness or ineffectiveness, or use.

        • Old Vet

          I had to put down a sick horse (for my sons granddad) with my 5.56 a couple of years ago. I was at point-blank range. Just as I squeezed the horse lunged. It hit him just below the eye on his front snout. It took him several minutes to expire. Should have used my .45, I guess.

  • RBK

    It would be good to see a chart that takes the middle ground for each caliber and overlays them…some reasonable average…and overlays 5.56, 6.5, 7.62×39, etc. Whatever the most common weight/grain in and 20″ barrel length to compare them, if there can be such a thing as “most common”.

    I am curious to see if the differences are relatively negligible when under 300 yards (supposedly when most engagements occur). If so, the military was right to just stick with the 5.56, and avoid the expense and logistical nightmare of switching calibers.

    • This series will wrap up with a big “battle royale” between all the calibers comparing them in all five dimensions, so stay tuned!

      • Blake

        sweet!

        • Also, I will at some point post my data for the geeks. I realize these posts have been shorter and less detailes than some people like!

          • Shocked_and_Amazed✓ᵛᵉʳᶦᶠᶦᵉᵈ

            Thank you Nat!

    • A Fascist Corgi

      I watch war porn videos almost every day on YouTube. Combat engagements past 300 yards is extremely common.

      • BattleshipGrey

        NM, read it wrong

        • ostiariusalpha

          It’s a metaphor (mostly).

      • Bill Maxwell

        The problem with m855 was actually because of the wrong twist rate and barrel length, Not the round. M855 was developed for a 20” 1-9” twist, 1-7 in barrels longer than 10” is not ideal for most loads capable of fitting in a STANAG magazine.

      • Old Vet

        A guy I met while working in a small gun shop related a story of having shot a Taliban at about 100 yds. with his M4 and the guy kept coming at him. He didn’t say where he hit him first, but said his platoon sgt. finally stopped him with his Beretta at about 10 yds. Heavy clothing, possibly drugs, who knows, but the guy was out to get him a G.I. The sgt.’s first shot, although wild, took out his ankle, and the next two went into his shoulder and back as he fell, so I was told.

    • ostiariusalpha

      That can be somewhat deceptive, if you aren’t careful. There are a lot of competing needs for different barrel lengths and cartridge loads: 10.3″, 14.5″, 16″, 18″, 20″ barrels, each one might favor a different caliber. Trying to arbitrarily “average” out for certain barrel lengths and target distances also squeezes out the ones that work best in applications that don’t necessarily overlap with where you’ve set your goalposts. There are also numerous awesome hunting bullets that don’t pass muster under the Hague Convention, and some some others that favor penetration over terminal effect, and yet others that really shine at distances well past a mere 300 yd.

  • thedonn007

    I need to get a 6.5 Grendel upper for my AR lower.

    • ostiariusalpha

      Yes, you do.

    • notalima

      Yes, yes, you do. Feeding it factory ammo will eat a bit of your wallet, but if you reload, it isn’t terribly costly. I reload the 123gr A-Max and get very good results.

      And the giggles it gives making tiny little groups makes up for the few cents extra 😉

      • uisconfruzed

        I’m shooting the 130g Bergers. This is the first six rounds out of my 6.5, and they were handloads. Lapua brass, 130g Berger VLD. the single hole was the target, the next five were in one hole at 100yrds.

        • Tim X

          Wow, the 5 look like 3. Awesome. That’s the kind of accuracy I’d like to be able to attain. What kind and length of barrel do you have? SAAMI 6.5G or LBC? I’m looking at AA upper, with perhaps a Shilen upgrade in 20″.

          • uisconfruzed

            It’s: 6.5 Grendel, 18” McGowen modified HBAR, dual fluted, glass beaded, hand lapped, Cryo stress relieved SS barrel; Syrac adj gas block, Mega ambidextrous billet receiver set, WMD NiB BCG with AA hard use bolt, Geissele Speed NM firing group, Magpul PRS stock w/monopod, Ergo grip, Seekins 15” guard, TBAC brake/can mount & Bushnell Elite glass.
            https://uploads.disquscdn.com/images/56b9fa2bb27c85dab18d60ea97ab6ceb0467ac0974c5ee0f4c7c9d82ea47bd62.jpg

          • Tim X

            Sweeet! I’m hoping I could get those accuracy results with a medium contour, probably 20″ for the extra 100fps, because I want to be able to carry it for miles. The Grendel is such a narrowly configurable round that I guess you need the length to get the velocity up. How much does that puppy weigh? I want to keep it at 8.2 lbs scoped unloaded or less.

    • Blake
  • ostiariusalpha

    It’s amusing to see how small of a difference there is between the performance from the 14.5″ and 20″ barrels. Not that the longer barrel isn’t clearly more energetic or faster, but the Grendel performs quite admirably from a shorter barrel. Kind of puts the lie to forum fairy tales that the Grendel only does well in 20″ or longer barrels. As with just about any cartridge, bullet design plays a much larger factor in ballistic behavior.

    • thedonn007

      I want an upper with a 16″ barrel. I do not want an SBR lower for the 14.5″ version.

      • ostiariusalpha

        Those high BC bullets are truly impressive from a 16″ barrel, that length is very popular with Grendelers.

        • DIR911911 .

          that length is popular with ALL rifles

          • c4v3man

            Yes, but what would the most popular length be if the unconstitutional NFA tax wasn’t passed? I doubt we’d see as many 16″ barrels if the NFA vanished tomorrow.

            That being said, 5.56 seems to need all the length you can give it, however it’d be interesting to see if you’d see a bunch of 12-14″ barreled AR’s for people who don’t care about the best performance, with 18″ being the more often recommended “optimum length” rather than 16″. Gun ranges would get a heck of a lot louder… except everyone would likely own a suppressor as well with no NFA in place, so probably not a big difference.

          • thedonn007

            Just think of the ear drums of children, Sound suppressors should be mandatory, not regulated.

          • Kivaari

            Mandated by a regulation.

          • CommonSense23

            5.56 with the right load can do wonders out of a 10inch.

          • Kivaari

            More wonderful out of a 16″. I like the SBRs, but a 16″ gives a great compromise. Original M193 peaked at 20 inches. Extensive testing resulted in a tuned load without shoving the pressures off the charts.

          • ostiariusalpha

            As it should be (except it isn’t that popular for short action or longer rifles), but there has been a rather sleazy campaign on forums for the past decade to misinform that the Grendel is not a good cartridge for barrels at 16″ and under.

      • disqus_sgMcKYCZZ3

        Pinned and welded my friend.

  • Giolli Joker

    It looks like the 123grs load hits the sweet spot in the shorter barrel.

    • LilWolfy

      I shoot 123gr from shorter barrels out to 1000-1200yds, on steel, mostly 123gr AMAX and 123gr Scenar.

      16″ and 18″ so far have not shown noticeable differences in velocity outside of maybe 12-20fps, and it can be in favor of the 16″ sometimes with the same load.

      I also don’t see myself taking my old bolt guns out for hunting anymore, knowing what this is capable of on large game even at intermediate ranges. Typical hunting distances within 300yds is usually DRT.

  • BattleshipGrey

    I’ve been looking into selling my .308 boltgun to either fund an AR upper or a Boss 1500 in 6.5 grendel. Brownells has the barreled actions and Midway has a good stock selection. Sounds like it’d be a fun project too.

    • ostiariusalpha

      6.5 Grendel AR-15s are pretty dang fun, but if you are a reloader, the 1500 will allow you to step beyond the factory cartridges’ self-imposed 52,000 PSI limit due to the hoop stress limitations of the AR barrel tenon. It’s possible to safely go straight up to 60,000 PSI for same nicely enhanced ballistic performance.

      • BattleshipGrey

        Thanks. I’ve been debating for a while but I’m really coming to the conclusion that I either need to be patient and build one gradually, or sell off the .308. I don’t currently reload but I will in the future. With the cash I’d get for the .308, I’d have a pretty good start to a Grendel boltgun. But if I build an AR upper the way I want it configured, it’d be a lot more money and only get me a little more than halfway.

        For the moment, 300 yards is the farthest I can shoot anyway, so that kind of makes me want to be more patient for now. Lots of little factors to think about.

        Love the input though.

        • LilWolfy

          I’ve owned a lot of .308s, and pretty much everyone I know has at least a couple. I finally realized that I no longer had a need for .308 Win, and have just been building more and more 6.5 Grendels.

          It turns the AR15 into a rifleman’s rifle, without any real recoil penalty. The performance on-target is noticeably different from the shooter’s perspective. They are a really superb match for each other when looking at weight and performance, with such little recoil, kind of like a perfect storm.

      • Giolli Joker

        What is a Boss 1500?
        Personally I’m in love with the idea of a handy rifle in 6.5Grendel on CZ 527 mini action.
        If I could, that would be my 6.5 project.

        • ostiariusalpha

          It’s a Howa 1500 with a Ballistic Optimizing Shooting System (BOSS), I believe.

          • BattleshipGrey

            Just realized the stupid autocorrect changed howa to boss? I hate typing on tablets. Another wrinkle I’ve hit is 6.5G AR uppers on arfcom equipment exchange are reasonably priced.

        • Shocked_and_Amazed✓ᵛᵉʳᶦᶠᶦᵉᵈ

          Thank Goodness someone asked. I was about to. Thanks Joker, the only 1500 I knew of was a Howard but the conversation was AR uppers so I was a little confused

      • LilWolfy

        I don’t think I would push it much with that Howa action, since it is pretty small in diameter. We talked with the importer and they felt the same way. There really isn’t a need to try to turn it into a .260 Rem or 6.5 Creedmoor.

        Even at 50ksi, with the same bullets, same barrel length, you’re looking at hitting the Grendel’s mv with a .260 Rem at 175-200yds, both of which are supersonic well past 1000yds. I think the lower recoil of the Grendel is what really makes it shine against larger case capacities, much like the old Steyr Mannlicher 6.5×54 M-S.

        Being able to see your shot placement without coming off the sights is worth more than unnecessary energy on-target to the efficient hunter. Where the .260 Rem does come into play is making steel ring louder at distance, or extending into long-range hunting territory for the rifleman and guide team who posses those skills.

  • micmac80

    6.5 Grendel graphs are fancy but compare apples and oranges , low drag match bullets vs military bullets.
    One thing that they forget to mention is that to a soldier a flat shooting 100-300m round is far more important for higher hit probability than some small gain down 600+m that is all due to the low drag match bullet.

    • iksnilol

      I presume that a round that drops less at 600+ meters will also drop less at 100-300 meters (IE be flat shooting).

      • micmac80

        No, because for the first part higher MV velocity of an for example .223 makes for flatter shooting , good high BC bullets retain their speed and energy better so can overtake the round using ‘draiger bullet) on that grounds alone but that only happens some 600 or so meters down the range at the distances soldiers cant hit a broad side of a barn anyway.

        • iksnilol

          So you are seriously arguing that a fast bullet with good BC is going to be less effective than a fast bullet with worse BC? At close range (300 meters) that is.

          Screw this, not drunk enough for this today.

          • ostiariusalpha

            At close range, it’s mostly a matter of which bullet is faster. A 7 gram 6.5 bullet going 759 m/s is going to be flatter shooting than an 8 gram bullet going 728 m/s, at least until around 400 meters.

          • iksnilol

            How much difference is there going to be between 759 meters and 782 m/s?

          • ostiariusalpha

            Heh, I ran some calculations and it’s more like 800 meters when the 8 g bullet surpasses the 7 g one. Deviation maxes out at about 6cm less drop for the 7 g, which is nothing to sneeze at.

  • myndbender

    How do 6.5 Grendel ARs behave w/ a steady diet of the Wolf 100gr, as that would be what I’d feed it a majority of the time

  • iksnilol

    I want a small bolt action in the caliber (IE CZ 527 switchbarrel). What length of barrel would be good for it (considering a suppressor that extends 10 cm past the muzzle)?

    • I would take that question to the Grendel forum.

    • ostiariusalpha

      Nate’s probably right. The main questions are the usual, what are you planning on shooting and at what distances? If you aren’t dragging it through brush, then you can go with a 50 cm barrel, otherwise a 40 cm barrel might be more wieldy.

      • iksnilol

        Was thinking switch barrel, so one 30-35 cm barrel with pinned 10 cm suppressor for brush and whatnot whilst another 60-65 for supah long distance.

        I just wonder how the cartridge behaves out of a 30-35 cm barrel.

        • ostiariusalpha

          There are some Grendelers with 14.5″ barrels, and they seem quite satisfied with its performance. You are going to be getting some more blast out of a shorter 30 cm barrel, but nothing overly intense. Still, I’d go with the 35 cm, just to milk the Grendel’s powder capacity a bit more.

          • iksnilol

            I am not worried about blast (pinned suppressor that extends 10 cm).

            But I could live with 5 more cm and have less wear.

        • uisconfruzed

          Bill Alexander’s favorite length is 18.5″

          • Stan Darsh

            That’s interesting, 18.5″ happens to be the barrel length DARPA found to be the best under the XM3 program.

  • I suspect the next major rifle will be based around a smart optic deigned for long range rifle fire and precision/airburst grenade use.

    The optic would be sort of hybrid between the Elcan 1-4 and the Steiner ICS, with ballistic calculator and integral laser range finder, calibrated to both the rifle out to 800 yards and grenades out to 300. 1x red dot for CQB, 6x for target ID and precision shooting.

    The doctrine will likely focus heavily on the use of precision grenade fire for targets between 50-300 yards, due to the ability of airburst G’s to defeat targets hidden behind cover.

    Rifle fire will be either for CQB, where things are too fast for precision G’s, or for distances beyond the range of the GL.

    An ultra high BC (.420+) 77gr .224 projectile built like the M855A1, but with an optional Tungsten Carbide tip, fired at 3,000-3,330 ft/s, would be my choice. This would keep weight per cartridge down, while offering improved range and power over 5.56×45.

  • ostiariusalpha

    If a cartridge is SAAMI approved and manufactured by Hornady, Federal, Lapua, Prvi Partisan, and Barnaul, and you’re still calling it a boutique round, something might be wrong with your definition. And that Barnaul ammo is about 30¢ a round.

  • Dan Hermann

    Check out my videos on you tube. 6.5 Grendel on steel. The 6.5 Grendel on steel II shows the trace of the bullet downrange and explosion of lead on steel targets out to 400. I shot at 500 but that target was painted white so you can’t see anything.

  • uisconfruzed

    I’m very impressed with mine! 6.5 CM is next

    • ostiariusalpha

      That’s what I went with. Love that 6.5!

  • cwolf

    Military looks at a variety of factors beyond cartridge performance: full-auto capability, manufacturing capability (over 1+B rds/year), fleet life cycle maintenance/wear, reliability in a wide variety of climates, cost, etc. Army ammo has no accuracy requirement because it costs more.

    Given the zillions to make a rifle/ammo change, there have to be significant/major advantages to get folks to open those checkbooks. Availability of brass and those costs may push design changes as much as anything.

  • Tim X

    Dang, I am so amazed that such a slow moving 6.5 cal projectile will take an elk at 390 like that. Good shooting young lady!! What projectile was used, and what is the MV? I’m deciding on components for a 6.5G now. Regarding elk, I was thinking my 270 BAR with 130s leaving at 2940 might not be enough so I bought a 7mmRM for which I’ve tuned 140gr Barnes @ 3200fps into .5 MOA loads. Hoping I don’t need 3 shots with those. The 6.5 will be for targets, deer, and pigs.

  • LilWolfy

    For the historical backdrop, I would say Arne wildcatted 6mm PPC to 6.5 PPC with the shoulder blown forward, whereas Bill Alexander and Janne Pohjoispää from Lapua developed the cartridge. The majority of the brass RDT&E involved a different set of case dimensions and metallurgy, with yield at 60ksi, giving a 10ksi buffer from working pressure.

    I see the Grendel more as a replacement for .308 for my own needs, with a bit better wind drift, and half the recoil.

    From a military perspective, it provides the option of having your standard format M4 or SPR, but with flight and terminal characteristics like M118LR, with higher round count per weight, while still being more than suitable for close range fighting. It’s basically about perfect for a DM or SASS weapon, while not giving up much for an assault rifle.