New Long-Range Wildcat for AR-15: the 6.5 x 40mm

Small Arms Defense Journal spent some significant ink profiling the development of a new AR-15 platform compatible long-range round. The 6.5x40mm (aka .264 Warrior Magnum) is not to be confused with the (relatively) common 6.5 Grendel. Developed by Mitch Shoffner, the 6.5x40mm provides performance close to 7.62x51mm NATO at short range and exceeds it at long ranges.


The 6.5x40mm would require a bolt, barrel, and potentially a magazine change. The principal differences between this and the Grendel are the x40 uses the smaller 6.8 SPC case diameter (.42″ vs .44″ of the Grendel) but opts for longer case length. It operates from M4 magazines, but for optimal performance, would require its own purpose-built feed lips. Further details on the differences between this, the 6.8 SPC and 6.5 Grendel are in detail in the article. 

As with anything, bullet design is an exersize in trade-offs. The 6.5x40mm is no exception, but for many shooters and military customers this benefits may be worth it. For a significant increase in range and simplifying logistics (no need for 7.62 DMR weapons), a 30% increase in cartridge weight, steeper cartridge drop, and small increase in recoil it may be worth it to convert.

Velcoity Comparison

In my personal opinion, the military is not likely to move from the 5.56 (especially with the new 77 gr. and new Enhanced Performance Rounds). Until the military decides to actually fight the next war instead of the previous one, development efforts of Wildcat cartridges will have to do for long-range AR shooters.

**All pictures courtesy of Small Arms Defense Journal.

Nathan S

One of TFB’s resident Jarheads, Nathan now works within the firearms industry. A consecutive Marine rifle and pistol expert, he enjoys local 3-gun, NFA, gunsmithing, MSR’s, & high-speed gear. Nathan has traveled to over 30 countries working with US DoD & foreign MoDs.

The above post is my opinion and does not reflect the views of any company or organization.


  • While I think the cartridge is very neat, I think Mr. Shoffner is a little off-base trying to market it as a military cartridge. The military is pretty happy with the two-cartridge system as it stands.

    • dp

      That may be true as long as military is not seriously pressed to think of some kind of rationalization (cost of keeping such vast military in general is enormous). Also, to keep in mind – the current array of calibers must be nightmare to logistics. There is only one way out of it – new cartridge.
      I understand where you are coming from – you are expert sport shooter and ballistician. Military criteria and preferences may not be the same into future.

      • I don’t know that I would consider myself an “expert sport shooter”, and there’s a lot I have to learn about ballistics.

        I simple don’t know how introducing a new rifle cartridge (with weapons and parts to go with it) will simplify logistics as many claim.

        • Tim Pearce

          It would if it replaced both 5.56×45 and 7.62×51, but then we would either have to pressure NATO into adopting our new cartridge or we wouldn’t be able to share ammo.

          • dp

            Europeans would gladly jump on that; look at previous British developments.

          • Really? If you talk with the Swedes, French, or Swiss, for instance, they are very happy with 5.56mm.

            The Germans might give you a different answer, though.

          • Even if we could get it adopted, there’s the problem of how to produce the new ammunition. The US has one ammunition plant – Lake City. Do you halt production of ammunition there for a minor ballistic benefit (and a large weight detriment)? Then there’s the problem of now having three cartridges in service. Ammunition change-over doesn’t happen instantaneously, the older weapons and ammunition remain in service long after the new ammunition and weapons are introduced.

          • 1911a145acp

            When ever does this “share ammo thing ” happen? 😉

          • I’ve heard some soldiers talk about pulling 7.62mm ammunition from belts to feed their M14 DMRs, but beyond that, it doesn’t seem to happen much.

            I would think that if the situation was dire enough that you needed to be pulling rounds out of belts to feed your infantry rifles, you would want a caliber that you could bring more of with you in the first place, like 5.56mm.

          • 1911a145acp

            I was referring to the posters “NATO sharing” reference- not sharing between US troops. I don’t think there would be any documented cases of us calling up Italian or German NATO coalition troops and asking to borrow some ammo or vice -versa. Soldiers seem to ALWAYS run out of ammo no matter what the caliber. Most rounds fired do not hit nor were they intended to hit enemy combatants. As to the example you offered of pulling MG ammo out of links to feed precision rifles-That eloquently demonstrates the short comings of the 5.56mm. Nearly no one uses it for a long range DMR or sniping round. It takes more little bullets to to the SAME job as bigger bullets. Having LOTS of them doesn’t make them more powerful.
            Is it possible to create THE compromise cartridge that can do the long range job and the short range job? It seems to me that one that DOES the long range job should excel at the short range job. The compromise cartridge seems to have eluded us so far.

          • Here’s a dissenting opinion on that, BTW:

            “For most modern combat, 300 meters is plenty far. I carried an M14EBR (Enhanced Battle Rifle) in Afghanistan, and I could consistently hit a torso-sized rock at 900 meters – at the range, with perfect weather conditions, a good firing position, on a stationary target at a known distance. In combat, with extreme heat or cold, unknown distances, hasty firing positions, adrenaline and moving targets, plus little annoyances like incoming fire, I would have been ecstatic to smoke a mofo at 200 meters.”

            I don’t really know what to think of this, but I can say I’ve heard virtually no experienced users tell me they felt they needed infantry rifles that could reach out past 500m (specialist sniper rifles being an exception).

          • 1911a145acp

            I agree that “normal” distances rarely exceed 300 meters… except when they do. The Brits seem to hold a counter opinion. Nearly every long arm in a squad is 5.56mm except for the occasional L7A2 GMPG- ( their version of the 7.62x51mm NATO 240 B) Seems the Brits were tired of being ambushed by multiple PKMs (7.62x54R) at 600 + meters. Effective counter fire could not be made with the 5.56 mm weapons and the lack of optics and pin point accuracy made the belt-feds largely ineffective as well. This led to the procurement of nearly 500 of the LMT – Lewis Machine Tool, L129 A1 7.62x51mm & ACOG 6x optic equipped rifles to address the shortcomings.
            ( Ironically the 2nd time the Brits bought a Lewis gun from us! ) Again, it seems obvious that a cartridge with long range capability should be able to handle short range as well.

          • I would counter this argument by saying that focusing on the range of engagements ignores the capability of the individual rifleman. Regardless of at what range infantry combat happens (it sometimes happens at very long ranges; there have been instances from the recent conflicts where indirect fire tables were used with M240 MGs), the rifleman is not a steady enough firing platform to hit point targets beyond 500m in combat. This is why the infantry squad is equipped with weapons like GPMGs, mortars, and – recently – recoilless rifles.

            Some would add the DMR to that list, but if we take Chris Hernandez at his word, even they are largely pointless past 300m, even in mountainous Afghanistan.

          • 1911a145acp

            Sorry- I’m confused. Your statement seems contradictory. Is cartridge performance unimportant or is the capability of the Rifleman unimportant? If 7.62mm with optics is “largely pointless” past 300m, then certainly all 5.56mm is, and improving any performance of the cartridge past 300m would be pointless.

          • I would restate it as “the usefulness of a gun system is limited by the abilities of its platform”. An artillery piece is a very stable and long-ranged platform, and its ammunition should reflect that. A rifleman is not, and a rifle’s ammunition should reflect _that,_ too.

            Crew served and dedicated automatic weapons can extend the effective range of the infantry quite a lot, though.

          • The capability of the rifleman to affect a target in combat is generally limited to – depending – between 200 and 500 meters maximum. Because of this, you do not get much out of issuing infantry rifles in calibers designed for ranges beyond this.

        • dp

          I am tempted to think, the issue is even wider and it includes weapon itself. M4 development may be considered mature (meaning you cannot go any further with it), but its own issues notwithstanding (1960s state of art), it simply limits consideration for any future round.
          It may be that there is enough potential to start from scratch for new system. As please, no more direct gas.

          • What problems do you feel there are with direct gas impingement?

  • Lance

    Still prefer 6.5 Grendel. Overall were not going away from 5.56mm and improvements to the cartridge makes it a good lethal round.

    • dp

      The 5.56×45 was intended for its tumbling effect as prime objective. To get to that it was necessary to keep barrel length at 18″ minimum. With later ‘fade’ of conversion to 16″ this is mostly lost. So, no benefit and lots of penalties. high time to start over.

      • Who told you that 5.56mm doesn’t tumble with barrels shorter than 18″?

        • Joe Liberty

          Some dumbass drill sgt or internet warfighter do doubt…

      • uisconfruzed

        The 5.56, just like other other rifled cartridges, will easily tumble when they don’t have a rapid enough twist rate to stabilize the round. The Vietnam era M16’s had something like a 1/14 twist, most modern rifles are @ 1/9.
        The 300BLK subsonic needs a rapid twist 1/8, or the round will trash a suppressor.

        • You’re mistaking tumbling in the air (“keyholing”) with tumbling when it hits the target, which is what dp is referring to.

      • petru sova

        you have got it backwards. A shorter barrel will develop lower velocity which means it is much more likely the bullet will tumble providing the rifling twist is also on the slow side.

        • Joe Liberty

          OMG NO! The tumbling of which you seek happens AFTER the bullet enters the target, not on the way to the target! SHM…

    • Nicholas Mew

      So do I but they could theoretically increase its power to Russian 6mm.

      • dp

        Yes, the shot in middle; 6×49 with steel case, muzzle velocity in excess of 1000 m/s; potent shot. Development temporarily put to ice in mid 1990s.

        • Muzzle velocity was 1100-1150 m/s (3,600-3,770 ft/s) with a 5 g (77gr) bullet, according to Max Popenker.

      • Raven

        What’s up with that weird groove above the case head? Not the extractor groove, I know what that is, the one that looks like the inverse of a belted case.

        • It’s an element of the steel case designed to solve problems of mild steel cases at high pressures (they have problems expanding, and can have case head failures). The groove gives the material a little bit of extra give during the case expansion phase.

  • Graham 1

    I would like to see a direct comparison to 6.5 Grendel.

    • Tim Pearce

      I honestly see so little difference between the two that such a comparison would probably be embarassing for them. The case of the Grendel is shorter specifically to allow for longer bullets. I’m surprised that they even tried seating 140gr bullets in the 6.5x40mm. The only advantage I see in the 6.5×40 is magazine capacity, and that will probably only be a small increase.

      • dp

        There is one potential problem with Grendel round – it pushes chamber stress loading to the limit due to increased case diameter. Actually, even in existing configuration the Safety Factor is 1.1-1.2 (case strength not consider). Use Lame’s formula to convince yourself.
        Increasing barrel O/D is not an option.

        • petru sova

          So if the Grendel round is unsafe because of its diameter then how about a Weatherby 458 Magnum?

        • NikonMikon

          so how do you solve this problem?

  • BOB

    6,5 PPC uses standard mags and bolt

    • sauerquint

      If you reply to this I would ask that provide a link to the cartridge you are referring to. I am only aware of .20, .22, and 6mm offerings in the PPC line. None of them use a ‘standard’ AR bolt. The case head on all 3 measure .445, compared to .385 of the standard 5.56 and .473 for 7.62×51. As for the mags, they may fit and feed from AR15 mags, but they aren’t standard to that either.

    • 1911a145acp

      Uhhmm nope- I don’t think so.

      • BOB

        don’t think what?

        • 1911a145acp

          Sorry- my mistake. I read your post as 6.8 SPC. 6.5 PPC is a great mid range target round. Others have noted the main issues seem to be lack of cases, limited case capacity, limited suitable bullets for the expected velocity range.The vast range and availability of inexpensive 30 cal projectiles, and the lack of cheap, plentiful 6.5mm in the U.S. make it an up hill climb for all 6.5mm projects.

          • BOB

            no problem, it didn’t help that I misidentified it as PPC when its really PCC. I get what you’re saying about projectiles, and while its true there aren’t many bulk opportunities to buy 6.5, you can still get them most place for .30 a projectile, not really a plinking, pray and spray round, but it would be more than affordable for target and marksman shooting. Case capacity is always the compromise with a .223 based cartridge, just the price of convenience.

  • ColaBox

    Great, another nice cartridge that wont be popular enough to ever be seen on the shelves. Im still waiting to see 6.8 and .300BLK in person. Well, here’s hoping.

    • BOB

      do you even reload, bro?

      • ColaBox

        Na dawg, I buy factory. Too much math not enough money to try. Plus when I make it, it goes wrong very fast. Im the kinda guy who will breath once into a balloon and somehow pop it.

        • BOB

          good to know your limits

          • Uncle Charlie

            Long distance? Funny the 6.5×50 isn’t considered a long distance round even with a 28″ bbl.

          • BOB

            6.5s all have freakish long distance potential, they are very interesting bullets.

  • I suspect that the modified Lancer L5 AWM magazines that Wilson Combat has offered for its 7.62x40mm WT would be preferable.

    • Seems to me like they wouldn’t fit right. 7.62×40 WT uses the .378″ 5.56mm case head, and I don’t think a .422″ case head would fit that well. They tried that originally with 6.8 SPC and found it lacking.

      • Sorry, my brain vapor locked when the article mentioned the use of standard M4 magazines.

        • Since you brought it up, did the Lancer AWMs actually need to be modified to work with 7.62×40 WT? I was under the impression that they were designed from the outset to work with that cartridge, but my memory on the subject is pretty fuzzy.

          • Clearly, Wilson Combat seems to think the rib modification is necessary. I know I’ve seen others comment that certain loadings of the .300 Whisper and .300 Blackout suffer interference between the 0.308″ projectile’s ogive and the forward rib of a standard 5.56x45mm magazine. The earliest articles on the Whisper noted that SSK recommended milling out part of the rib on metal magazines.

          • Sorry, my question was unclear. I was asking if there actually were two different L5 AWM magazines, one for 5.56 and one for 7.62×40. A quick googling says yes, there are. I’m looking at the ones for sale through WT’s website, and while they say they have been “de-ribbed”, it’s not evident that that is actually the case in the accompanying image (the magazine in that image is clearly marked 7.62×40 WT and loaded with that cartridge), so the magazine isn’t just a stock image of a 5.56mm AWM.


            They are talking about the reinforcing depression that runs vertically along the size of the magazine, right?

          • The forward rib in a standard AR-15 magazine tube is sized to control the side-to-side movement of the 5.56x45mm case neck, and is positioned to control the forward movement of the case via its shoulder. This rib in the 7.62×40 WT L5 AWM magazine is slightly shaved internally for clearance.

            The following link has a photo of a modified 20rd aluminum magazine that has the forward rib slotted for long-loaded .300 Whisper. You can easily imagine how adding an extra 5mm of case length could complicate the clearance issue.


            The next link displays 5.56mm magazines, including the Lancer L5 AWM, with the forward ribs modified for use with the 7mm TCU-AR.


          • Awesome, thanks for the links!

  • Gyufygy

    You know, I keep thinking about getting into some of these boutique rounds like 6.5 and 6.8 for the improved performance over 5.56. Then I remember I put a grand total of 100 rounds of 5.56 through my rifle last year, I’m not high speed low drag, and my range only goes out to 200 yards anyway, so reality comes crashing back and I stop trying to be an ammo hipster.

    Still, it’s fun pondering the options. :p

    • 6.8 SPC Shooter

      Come check out our 6.8 SPC forum at and check out some of the setups us guys over there have and chat with some 6.8 SPC shooters!

    • C-Will

      Same here… I totally understand where you’re coming from. I’ve been having a ‘jones’ about 6.5 Grendel & 300 Blackout but I know I really don’t need to convert any of them.

  • Steve Truffer

    Rather than a new cartridge, what about a better load design? M855 was meant to pierce a soviet helmet past 600m at the exclusion of all else, m855a1 is… aside from hazardous, I don’t know. The Mk262 is incredibly accurate, but it seems lackluster on impact. The Russians have the 7N6(2) round, which has a jacket the size of a 77 grain bullet, but weighs in at only 55 grains. It has a hollow nose cavity, is very back-heavy, upsets quickly and violently, has a hardened steel rod for comparable barrier penetration to the m855, has an incredibly high ballistic coefficent, and retains more energy at distance than any 5.56 load. Why not copy that bullet design, get it to push 3000-3100 fps from an M4, or more from a rifle proper (with good accuracy), and make everyone happy?

    • dp

      Its good to keep in mind what someone else does, but lot could be done just by re-arranging M855 to new requirement. In concrete terms and for relatively low expense of rebuilding the fleet, case can be reduced by 2mm to 43 O/L. That in turn would allow to use longer bullet (keep the bore size) with better BC and mass at around 100gr. That would be a qualitative jump without doing much (well yes, you’d have to take 2mm off back of the barrel plus shoulder and re-torque extension). So, some minuscule drop in velocity, but longer carrying energy potential plus better penetration. Same gun, same magazine. Done.

      • Steve Truffer

        Yup. Like the 6.8 vs 6.5 comparison. 7N6 just struck me as being nearly identical in use and diameter, and all the proportions are already there. Or, if for some reason, there is an issue with the taper, adjusting to use the mk262’s jacket would give the same good accuracy, resolve the penetration issue, exacerbate the effect on tissue, and increase flatness. seems like they could swap the pill in the 262 loading and , sorry to sound like an idealist, but solve most solvable problems. Still can’t wrap my head around why the higher ups (who wouldn’t use it anyway) wanted a round with poor accuracy, poor terminal effect, more drop, more recoil (relative to 55gr loads), and higher cost, all to penetrate a target 1/4 the size soldiers are trained to hit, at twice the distance they are trained to shoot.

        • dp

          There may be only one tangible answer to your question: lack of motivation. Look at it this way – if you have lived in competitive environment, as most od us did or do, you have no choice but to atone to it. They don’t – job secure, pay adjusted to life expense index plus beefy pension.
          Now, since you are open to free thinking, let’s imagine you’d have TWO governments competing with each other (something like idea of competing currencies) – for everything. Oh man, paradise of Earth!

          • Steve Truffer

            If only. Once I’m out of school, I might just have to give a few manufacturers a call. And get an AR. Love my AK and 5.45 goodness so much.

          • dp

            No one can blame you for that.

        • 1911a145acp

          Because they ARE the higher ups…..

        • Remember: Small arms is 10% ballistics, 90% logistics.

          • Steve Truffer

            I’d say 10% ballistics, 30% logistics, 60% politics.

          • Politics is implied, of course.

            But even if you get through the politicians, you’ll have to go through the engineers saying “why do we need a third caliber? What we have works fine and fills our needs…”

          • Steve Truffer

            Hence my suggestion for improving the existing loads. faster, flatter, more extreme upset, better barrier penetration

          • That perspective – in my opinion – focuses far too much on the ballistics of a cartridge.

            In the big scheme of things, even significant gains in ballistic terms are peanuts when compared to their cost in logistics.

            Chasing the ideal is fine, but when it conflicts with practical and logistical concerns, it will always lose.

          • dp

            I followed on your discussion with Steve and as a result coming out with substantial deal of enlightenment. I am not sure if it belongs to me to do judgement in that direction, but just for my own part, I’d say your presence is most useful and productive.

          • Hey man, I’m just some guy on the internet. 😉

          • 1911a145acp

            Damn you Nathaniel F.! There you go again squashing our lofty concepts of the ideal combat cartridge with your Ice cold bucket full of real world ballistics, cost benefit analysis, logistics and the sobering reality that Small Arms on the modern battlefield really don’t get a whole Helluva lot done……;-)

          • Hey, no problem! 😉

          • 1911a145acp

            All true- because the engineers are not trying to drop a doped up Taliban bomber with a 22 cal projectile (s) at 2500 fps through auto body sheet-metal and laminated safety glass…..

          • Except that doesn’t reflect the considerable amount of work that has been put into improving the terminal effect of calibers. Again, see the fleet yaw study I linked to earlier. What they found, was that it didn’t matter what caliber you were shooting, all of them exhibited this yaw problem within 50m. If your round isn’t dumping its energy into a human target, it won’t be effective against that person, regardless of whether it’s .22, .27, or .30 caliber, whatever.

            So they made real improvements in that area with the M855A1 and Mk. 318 cartridges. Which has me asking, exactly what does a 6.5mm cartridge firing a pedestrian FMJ have to offer, exactly, except higher numbers on a chart?

          • 1911a145acp

            Are we to limit our focus only to projectile yaw and tissue disruption? I can’t image a logical argument that states that a 50 BMG round that deposits very little “energy” and yaw into it’s human target would be considered ineffective. I would assume that any newly developed 6.5mm projectile would have, not only FMJ, but Steel core, AP, Tracer versions as well. As I stated in a earlier post we are asking the little 22 projectile to do a lot of different, sometimes diametrically opposed jobs. It would seem that a larger slightly heavier bullet could be made to do those job better. However, an only slightly larger slightly heavier bullet may not offer any significant gains. Which brings us back to your point that I agree with- a better engineered and improved 5.56x45mm NATO round is likely the best path – all things considered. What is ANY new cartridge going to do magically different inside the common 300 meters engagement distance?

          • Consider that a .22 caliber projectile is very similar in diameter to a .24, .26, .28, or .30 caliber one. These characteristics matter, of course, but if you want to discuss the permanent wound channel, the caliber will make almost no difference within this band. This is why you absolutely have reports of 7.62mm or even .50 caliber projectiles hitting people and not phasing them. These weapons are rarer than 5.56mm ones, and typically used by much more skilled personnel, so the accounts are rarer, but they still exist. Here’s an example:

            Likewise, bullet weight does not factor into the terminal effectiveness equation, except in two formulas: Sectional density, and energy. Sectional density informs penetration, and with M855A1 5.56mm seems to be more than adequate in this respect. In terms of energy, what matters for incapacitation isn’t retained energy at range, but the energy deposited into the target. 5.56mm was having difficulties in providing the consistency desired in this area, but preliminary studies show M855A1 to have solved this, and field reports are positive. Might a 6.5mm caliber be an improvement in this way, with similar bullet construction? It might be, but you can’t kill someone any more dead, and 5.56mm appears to be meeting the needs with the new bullet construction. Certainly, I do not feel that over the ranges at which infantrymen with rifles are most effective, the 6.5mm provides any real tangible benefit.

            This essentially seems to agree with your post above.

          • 1911a145acp

            I think we are in agreement on nearly every point concerning the realities of 5.56x45mm NATO. It is VERY unlikely to be replaced in the M-16/ M-4/ M249 platform-ever. It is interesting to ponder a new cartridge based on current understanding that could replace 5.56 & 7.62mm in their current infantry roles. I suppose near future developments could make it a hyper-velocity .17 or 20 caliber round with a projectile that could do it all ( so claimed HK) like the G11 4.7x33mm DE 11 round.
            Do you have links the studies about improvements and field effectiveness of the M855A1 you mentioned?

          • The field reports come from this “M855A1 Media Day” presentation. Take them for what they’re worth, but they’re at least encouraging:

            Unfortunately, there isn’t really a single study I can link you. Somewhere in this comments section, I linked the fleet yaw study that laid the groundwork for the M855A1 requirement that it needed to be yaw-independent. I also linked Major Dean’s monograph somewhere around here. Collating from several powerpoint presentations and PDFs on the subject, it seems ARL did a study which hasn’t been released yet and determined that M855A1 was better at depositing energy than M80 Ball at all ranges, so that’s also encouraging.

            I really would like to have more hard data on M855A1, especially of the kind that could refute/confirm some of the objections to the round, such as it reducing the barrel life of the weapons it’s used in.

    • 1911a145acp

      Sounds great- sign me up- but how are you going to get 3100 fps out of an 14.5 inch M-4 barrel? The main problem with any SIGNIFICANT 5.56x45mm upgrade is you STILL have a 22 caliber bullet trying to get all sorts of tactical penetration done. Helmets, Body Armor, vehicles, sandbags, walls, mud huts etc.

      • Steve Truffer

        55 grain 7N6 scoot out of a 16 inch barrel @ 3000 FPS. The 5.56 has a goodly bit more capacity. Modern powders, the extra room, and the Army’s lack of concern over jacking pressures up by 15K PSI should compensate for the added length of the pill. If the design is good enough for the 7N6 to go through 1/4 inch 70 hrc steel plate, I think its as good as can be expected from a ball round.

        • A bit of a tangent from what you’re saying here, but the Russian 7N22 5.45mm and Chinese DBP-10 5.8mm steel cored AP rounds seem decidedly optimized for penetrating hard targets – even Chinese tests confirm the 5.8mm performs worse against soft targets than either 7N6 or M855. M855A1 is not optimized for this, instead it is intended as a “do everything” round, capable of penetrating light barriers (mild steel, windshields, walls, etc) while still being capable of ready upset and excellent energy deposition in soft targets.

          While I feel that the A1’s bullet design is decidedly superior to that of M855, it is fundamentally a compromise when compared to dedicated light armor penetrators such as 7N22 and DBP-10.

          Though it’s further worth noting that ARL tests found that at no range tested (out to 1,000m) was the M855A1 able to be stopped by “soft” body armor.

      • M855A1 seems pretty good to me. Big honkin’ steel core, 2,970 ft/s from the M4, multi-part construction implying breakup on impact with soft targets.

        If not that, Mk. 318 also seems like a step in the right direction.

        There’s a lot of design space for 5.56mm.

        • Steve Truffer

          IIRC, the steel penetrator is shaped like a polymer ballistic tip, and weighs only 15 grains. It also has a peak pressure of ~70K PSI – proof load pressures, which are supposed to be a 1-2 time thing for a barrel, and the worst case scenario. Not what you shoot on a regular basis.

          • Dunno where you’re getting you’re info, but you’ve been misled. The steel penetrator for M855A1 is roughly twice the size of that of M855, almost half the volume of the projectile itself. You can see a picture of it here:

            Note that the bismuth slug (labeled “alloy” in this picture) has since been replaced with a copper one of the same size. As you can see, the steel penetrator is very large.

            Also, the round does not product 70,000 PSI nominal (pressure fluctuates due to many factors, see below). It produces 62-63,000 PSI, about 5,000 PSI higher than M855. A study from 2006 showed that the propellant used in M855 – WC-844 – was not as temperature stable as desired, producing almost 90,000 PSI in the chamber of a barrel hot after extended firing. Following this study, the powders in Mk. 262 were replaced with a more temperature stable one, and the follow on M855A1 and Mk. 318 rounds both utilized more temperature stable powders – in the case of the A1, a powder called SMP-842. In other words, M855A1 produces slightly higher chamber pressure, in exchange for avoiding pressure extremes that result from hot barrels caused by extended automatic fire sessions.

            Here is the presentation regarding temperature stability in 5.56mm small arms:

          • Steve Truffer

            Hmm, digging at my sources, the 70K was after 5, 20 round mags. This definitely makes it look better than what I saw. Thanks for the correction. Wonder what it could do with tungsten?

          • 70K after 5 20 round mags is fantastic temperature stability performance, BTW. I hadn’t actually seen that source, could you share it?

            While I’m sure it would perform better with tungsten, the Army already has a dedicated tungsten penetrator round – M995 – and tungsten is too critical a material (and too hard to work with) for general issue.

            I agree, though, it would be scary as heck to have a tungsten-cored M855A1 variant.

          • Steve Truffer

            Warriortalk.. Holy crap, never again will I post while the doc has me on 15 mg hydrocodone. 20 round mag, 5 shot strings. My apologies Nate. From what my medicated mind tells me, Corbin Swaging said something about atomized tungsten powder being 1.4 times the density of standard lead. Shorten that sucker up, drop the pressure for better barrel life, or push it back up and see what scary speeds they can cook up.

          • Steve T., I empathize. I’ve broken enough bones and had enough teeth pulled to know what you’re going through.

            Unfortunately, tungsten powder was tried as a lead substitute very, very early on in the M855A1 program and found undesirable for two reasons. The first was that tungsten is a heavy metal and retains most if not all the environmental concerns that lead does (more on this in a minute). The second was that the tungsten powder variants of M855 that were tested resulted in the rounds tumbling in flight and keyholing.

            If you’re interested in M855A1, there’s a great monograph written by Major Glenn Dean, who worked on the program from 2005-2006, and was involved indirectly until 2008. It is called “In Search of Lethality: Green Ammo and The M855A1 Enhanced Performance Round.” It can be found on Major Dean’s Smashwords page, available for free:

          • Steve Truffer

            Thanks for the words and words of an authority.. Costocondritis bad enough to shift the sternum hurts like something not to be said in polite company.

          • You’re welcome.

            The environmental aspect of the M855A1 round has been repeatedly mis-characterized in the media and on forums, in no small part due to the Army’s own efforts in concealing the purpose of the M855A1 program. Originally, the program started out as a lead-free 1:1 replacement for M855, with exactly the same projectile design, only with a substitute for lead included. The reason for this being that the Army was finding the ranges it could use for training increasingly limited by environmental regulations. In an effort to comply with these regulations, they wanted a lead-free round so that the number of training ranges available to the Army would be significantly increased* (always a good thing, IMO). This stage of the program involved the early tungsten experiments. However, in a 2005 meeting, the Infantry Center representative gave the program managers the straight talk: What was needed was more effective 5.56mm ammunition, not a green round. Essentially, the program became an ammunition terminal effectiveness program, deliberately dressed up as an environmentally friendly project in an attempt to fly under the radar of Hague Convention violation concerns (this is not to say that the round isn’t Hague compliant, just that they were worried that they could get sunk from that angle). There’s a whole lot more to the story, which you can read about in Major Dean’s monograph.

            *The Army did the same thing in the late ’30s, when they switched from the 173gr boattailed M1 Ball .30-06 cartridge to the 152gr flat-based (and shorter-ranged) M2 Ball, in another separate effort to exploit more ranges for training.

          • Steve Truffer

            Ah, that clears a bit of my fogged mind. Elsewhere I made the remark about using a 7N6 patterned projectile to address some observed shortcomings of the well respected mk262 round. I thought that if many countries can make and sell a round so feared and respected for such a low cost, we might also be able to benefit from such a design, without prohibitive expense, especially with the greater capacity of the 5.56.

          • Army studies on projectile yaw (the primary wounding mechanism of the 7N6) showed that regardless of the size of method of construction of the projectile tested, all small arms projectiles exhibit what is called the “fleet yaw problem”, that is that within the first 50 meters of a projectile’s travel, while it is settling down in its stable flight pattern, the angle of yaw of the projectile varies wildly, which can cause through-and-through wounds, or can cause ready upset and massive tissue disruption. They did not find that caliber, construction method, or any other factor influenced this phenomenon. One of the projectiles tested was the 5.45×39 7N6.

            Therefore, I do not feel I can conclude that the 7N6 projectile is any “better” than M855 from a terminal effectiveness standpoint, as they both exhibit the same yaw characteristics, while M855 will often fragment (and 7N6 rarely does).

            It was the culmination of these studies that formed the basis for the “yaw independent terminal effect” requirement for M855A1.

            Here’s one of the studies:

          • Steve Truffer

            A talking library, awesome. Been great learning from you, but I need sleep.

          • I keep a folder of relevant documents. 😉

          • Also, consider that, according to the Army Research Laboratory, M855A1 exhibits superior penetration and energy deposition characteristics at all ranges vs. M80 Ball. This sort of statement is difficult for me to ignore, since I consider the ARL to be an eminently trusted source, and not typically a mouthpiece for moral-boosting propaganda.

            The guys who worked on M855A1 seem right proud of it as a combat cartridge and a step up from M855 in every way. Given what I’ve read about the program, I have a hard time not feeling that enthusiasm myself.

          • 1911a145acp

            Outside the U.S. Army there seems to be much criticism of the M885A1 cartridge as being too expensive ( 32 Million in costs thus far) and too inaccurate ( the core being temperature sensitive- expansion/ contracting /fracturing) I have only seen it and never shot it. Perhaps it will develop into a great improvement. Time will tell.

          • The original bismuth core was temperature sensitive. If the copper core is too temperature sensitive, as well, then that whole green ammo thing is basically bust. I doubt there are any problems with copper, though.

            The $32 million figure was the total cost of the development program, which, besides being a drop in the bucket by US arms development program standards, was fairly extensive, if Major Dean is to be believed. His description of it makes it sound less like a program to develop one kind of ammunition, and more of a comprehensive terminal ballistics study that eventually resulted in a cartridge standard.

    • Lt. Dan

      Because it was invented here! The Pentagon generals have to re-invent the wheel.

      • Lt. Dan

        That should read….”WAS NOT” invented here.

        • You can actually edit comments in disqus, FYI.

  • ClintTorres

    Even as an owner of a 6.5 Grendel, I think this is a great idea. There are few disadvantages to using high-BC projectiles.

    If the low-drag, high-BC bullets can be seated to mag length and produce the velocities in the table above, than it’s a winner in my book(virtually identical to the 6.5 Grendel).

    • Jeff

      Except because of their extreme length the bullet has to be seated very deep in the case occupying powder capacity.

      • ClintTorres

        Yes, that is why Alexander/Brennan chose the short and fat .220 Russian/6mm PPC case for the grendel…or so I’m told.

  • dp

    That cartridge looks just right proportion-wise; you really have to wonder why 6.8SPC and 6.5Gren had to be necessary to get here. By judging potential of this cartridge and its intentions it is of benefit to look at something modern and comparable. There is only one at the moment – Chinese 5.8×42 for combined rifle and GPMG (with heavier bullet) use. Russians had long time ago developed 6mm shot but did not act on it.

    • While I rather like that little 6.5mm (it’s cute!), the projectile construction of a round tends to count for a lot more than its ballistic performance. Given that the 6.5x40mm is being advertised with 120gr FMJs of a fairly pedestrian design, and that advanced 5.56mm projectiles in the form of Mk. 318 and M855A1 have already been fielded, it feels to me as though the 6.5×40 has rather missed the boat on being a real military round.

      • dp

        In light of previously presented rationale and wealth in inner knowledge you posses, I admit that there is lots to receive from you. I value your interest in discussing with me, although my arguments may sound bit on entertaining side. Thank you.

  • Mike F

    It’s pretty loaded to compare ball 7.62 to high BC long range bullets in their chambering.

  • 1911a145acp

    Been experimenting with 6.5/223 off and on for approx 3 years now. With Vihtavuori powder my gunsmith is getting 2800 fps w/ 90 Berger bullets out of a 20 inch custom bored SAVAGE bolt action switch barrel,2700 fps out of a custom 18 inch ACR w/ brake. 2580 fps w/ 105 VLD Bergers and warmish loadings. 5.56 magazines really limit max OAL. 6.5x45mm certainly has similar simple switch ability like 300 BLK and much potential left in it.

    • dp

      Very good thinking and plausible effort! Would you have some picture to show? Thanks.

      • 1911a145acp

        Cartridges in LH image are l to r; Federal .223 55 grn soft point, 6.5/.223 with 95 grn. Hornady V Max, 300 BLK, with 125 grn. Ballistic Tip. Rounds in MagPul magazine are 90 gr, Berger VLDs. OAL is just about at the limit for clearance but these rounds function perfectly in MagPul mags. I have another barrel in 300 BLK-couldn’t wait on Bushmaster anymore.I can shoot all three out of the Bushmaster.

        RH image is of the Bushmaster ACR 16 inch 6.5/.223 barrel with muzzle brake/flash hider “device”. OAL on that barrel is 18 inches. 90 grain Berger VLDs right at 2700 fps, warmish 105 grain bullets at 2550 fps.
        In the 20 inch SAVAGE barrel I have seen chrono slips of 2818 fps avg.
        The Hornady 95 grn V-Max bullet is an good accurate all around performer. In a Remington 700 bolt action .260 Rem caliber and a good charge of RL7- I have seen 3300 fps with this bullet- explosive results.

        • dp

          Excellent piece of work; thank you!

      • 1911a145acp

        Cartridges in LH image are l to r; Federal .223 55 grn soft point, 6.5/.223 with 95 grn. Hornady V Max, 300 BLK, with 125 grn. Ballistic Tip. Rounds in MagPul magazine are 90 gr, Berger VLDs. OAL is just about at the limit for clearance but these rounds function perfectly in MagPul mags. I have another barrel in 300 BLK-couldn’t wait on Bushmaster anymore.I can shoot all three out of the Bushmaster.

        RH image is of the Bushmaster ACR 16 inch 6.5/.223 barrel with muzzle brake/flash hider “device”. OAL on that barrel is 18 inches. 90 grain Berger VLDs right at 2700 fps, warmish 105 grain bullets at 2550 fps.
        In the 20 inch SAVAGE barrel I have seen chrono slips of 2818 fps avg.
        The Hornady 95 grn V-Max bullet is an good accurate all around performer. In a Remington 700 bolt action .260 Rem caliber and a good charge of RL7- I have seen 3300 fps with this bullet- explosive results.

        • This very closely resembles the 6.5×42 MPC designed by SSK several years ago:

          They have so far had very little success with it, unfortunately for them.

          • 1911a145acp

            Thanks for the link. We are all whipping the same tired run-out old horse here. It is interesting to experiment. New powders and projectiles can give any of our cartridges a SLIGHT performance boost on paper. There is just not enough case capacity and barrel length available and we can’t change the simple physics involved.
            I think we will be with brass cased ammo and the aluminium M-4 platform until a new-mostly plastic small arms platform and telescoped plastic cased ammo will make the ” Old School” brass cartridge/ metal gun platform no longer economically viable. just my 2c

          • I hate to break it to you, but telescoped ammo isn’t going to get off the ground, due to a flame-cutting problem that destroys the barrels. 🙁

            However, I would expect exotic case materials (aluminum, plastic) in the future, once the materials science on those gets worked out.

          • 1911a145acp

            These fellows seem to have gotten a few feet off the ground….


          • LSAT has some test platforms, but they’re running into these exact same problems. If you read some of their presentations available through DTIC, they talk about the flame-cutting problem.

            It’s an interesting effort, but they’ll either have to resort to exotic barrel materials, or change the ammunition form factor to something that doesn’t exhibit the flame cutting problem (either conventional layout ammunition, or some kind of semi-telescoped or saboted configuration).

            The reason this happens is that a lot of gas escapes past the bullet while it’s nested in the case. This means that LSAT ammunition uses much more propellant than normal, and wastes it burning the barrels up. While I am in favor of the LSAT program continuing as a research project, I’m not really holding my breath that telescoped ammunition as we currently know it will get past these issues.

            ..Which doesn’t mean tomorrow’s ammunition looks like what we have now with the case material swapped out.

  • jonspencer

    When the DoD finds the billions of dollars that it would cost to change over to a new round, then maybe one of these would have a chance to be selected. And I do mean billions.

  • SidViscous

    Okay, I’m sold. But where are the chamber reamers, barrels, dies and bullets? I can’t find anything.

  • phil

    6.8 SPC shooters come join us over at our new 6.8 SPC forum!

  • Blake

    Whatever this guy was trying to accomplish would most likely have worked equally well with one of the existing AR-specific wildcats out there. If 6.5gren & 6.8SPC wouldn’t do it for him then he would likely have been well-served looking at the established 6x45mm community rather than dreaming up yet another “tactical” wildcat…

  • Lane Crawley

    The 6.2 SPC would be better. Take the 6.8 spc neck it down to the 243cal bullet. An AR round in 243 caliber busting 3600fps. Nothing weve talked about on this forum will out perform the 6.2 SPC cartridge.

    • 3,600 ft/s? What, is it firing 50gr bullets!?

  • uisconfruzed

    I still don’t see any benefit of this ‘magnum’ round over my Grendel at 230 fps slower with the same 120g Norma round- much more flatter shooting.

  • 6.8SPC Shooter

    Just stick with the 6.8 SPC! Check out !

  • petru sova

    I would take the .260 Remington any day over all the other 6.5 guns that are chambered in the AR 15 guns.
    One must remember that the original idea behind the 5.56 was low recoil to enable the operator of the weapon to be able to control it better in full auto fire. The larger calibers cancel this advantage out totally. One must also realize that the new 5.56 ammo has superior penetration and contrary to Gun-writer myth it is not bullet diameter that kills rather it is shot placement and penetration.
    In the year 1900 Agnes Herbert a world wide hunter wrote that she no difference what so ever between her 45 caliber elephant rifle and her 6.5 mm Mannlicher rifle in regards to killing power. She was one of the first people to contradict the blow hard gun writers of her day and teach people to shoot not with one eye closed but with both eyes open. Since she shot and killed hundreds of big game animals she was more competent to give advice than most hunters or gun writers back then or of today.

    • maodeedee

      The only problem is that the 260 rem is NOT chambered in “AR 15” guns. any cartridge with a .308 case head size can only be chambered in “AR 10” guns which are bigger, heavier and cost more money and don’t use AR 15 magazines.
      if you wanted a more powerful 6.5 in and AR 10 sized gun, you might as well go with a 6.5 x 284.
      But for the best all around compromise it would be better to stick with the limited capacity .223 case and maybe neck it up to 6mm and load it with 100 VLD grain projectiles to get the best combination of bullet weight, velocity, sectional density and ballistic coefficient.

  • ⊕RussR⊕

    why not include 300blk on the list?.. no bolt change, no mag change…

    • .300 AAC Blackout is an interesting concept, but as a dedicated supersonic round, it does not out-perform 5.56mm in any respect, except close-range energy provided, in which it is only slightly superior (~1850 J vs. ~1650 J from 14.5″ barrels). It carries with it significant downsides in terms of trajectory at medium ranges, as well.

  • maodeedee

    The 300 blk has the major advantage of using standard 5,56 mags and 5.56 bolts. basing a 6.5 on a 6.8 case gives you a little more case capacity than the Grendel but if your;’e going to have to use different mags and a different boltface I don’t see any advantage over the Grendel unless 6.8 mags are more common and less expensive
    When the 6,8 was first developed, it SHOULD HAVE BEEN a 6.5 in the first place. That way the same weight bullet would have greater sectional density and a better ballistic coefficient.
    and that’s the advantage of this new chambering, except that it isn’t any better than the Grendel because both require non-standard mags and a bolt change.
    I think a better compromise might just be to neck the .223 case to 6.5 and you’d have a 6.5 TCU which is a pretty good cartridge firing a heavier projectile than is possible with the .223/5.56.

  • Wayne H.

    I thought Hector Rojas designed the .264 Warrior Magnum. And, being that’s parent case is the 5.56, the rim diameter is the same, the rim thickness is the same, the case diameter is the same, and the case taper is the same. Would that not equate to only having to swap barrel instead of swapping bolt, barrel, and magazine like with the 6.5 Grendel and 6.8SPC?

    • Yes, they are different cartridges; I think Nathan S. confused them. The 6.5×40 Shoffner is based on a 6.8 SPC case, and requires the same parts to convert an AR-15.

  • supergun

    I keep looking at the 308, AKs, and all the other fancy rounds. And I like them all, especially the 308 which I think is the perfect round, next to the 5.56. Dollar for dollar, with all the factors being figured in, you can’t beat the AR 15.

  • PanZr

    I’ve been working with a 25-223 wildcat along with some other folks. Pushing a 87-90 bullet to 3000fps which probably will go higher when newer powder are ever in stock.:-( Even with current powders it easily is equaling the much larger 250-3000/250 Savage cartridge. Only thing needed was a barrel change.

    • I suspect you’ll find under controlled conditions with standard pressure limits, and with short barrels, those velocities won’t look so good.

      There’s no “magic cartridge”; if you’re getting numbers that don’t make sense for the case you’re using, you haven’t stumbled onto a “sweet spot”, you’re loading it too hot (or your internal ballistics computer is having a bad day).

  • Mitch

    No specialized feed ramps are needed. Standard M4 ramps were used in all AR rifles with no problems. The case is 1mm longer than the Grendel, this allows any 6.5mm bullet can be seated and a COAL of 2.25″ can be maintained for AR15 magazines.