7x46mm UIAC (Universal Intermediate Assault Cartridge)

Cris E. Murray helped design the 6.8mm SPC cartridge for SOCOM and considers it to be the best cartridge for the AR-15 platform and similarly sized weapons. The problem with the 6.8mm SPC, and similar cartridges like the 6.5mm Grendel, is that their performance has been constrained by the necessity of the cartridge to be able to be chambered in a M16 or M4.

7x46mm UIAC in AR-15 magazine and AR-10 magazine.

In his spare time Chis has been developing the ultimate military cartridge which he calls the 7x46mm Universal Intermediate Assault Cartridge. The design is based on the 7.62x45mm Czech cartridge.

The 7x46mm is designed to replace both the 5.56mm and 7.62mm NATO cartridges. It is low recoil and so can be used from carbines, but has long enough range to be used in machine guns and marksmen rifles. Its overall length has been optimized so that guns chambering it would be bigger than an AR-15 but smaller than a AR-10.

The below photos show how it compares with the 6.8mm SPC. Note: the 6.8mm round was fired from a 12″ barrel, while the 7x46mm was fired from a 16″ barrel.

6.8 mm SPC (Hornady 115 gr OTM) fired from a 12” barrel at 100m.
7x46mm (Hornady 120 gr OTM) fired from a 16″ barrel at 100 meters.

The below ballistic graphs are for a 7x46mm UIAC loaded with a 130 gr bullet traveling at 2650 fps.

Murray has stated that the 7x46mm is designed to …

  • used a 130 gr. FMJ projectile having a length of 28.5mm (1.1220 in.) and a BC of .411 or better.

  • have a maximum cartridge over-all-length (AOL) 64.262mm (2.530 in.).

  • be used with 7mm Mauser bore diameters of 6.98mm bore, 7.24mm groove, having 4 grooves at a 1:297mm (1:11 in.) twist rate.

  • be used in 7mm American bore diameters of 7.04mm bore, 7.21mm groove provided proper reamer bushings are used.

  • to have the same pressure specifications as 7.61x51mm NATO/EPVAT.

7.62x33mm, 5.56x45mm, 6.8x43mm, 7.62x39mm, 7.62x45mm, 7x46mm, 6.5x47mm, 7.62x51mm, 7.62x63mm

This cartridge seems to be more a reference design than a practical cartridge. If the military do not want to switch to another 5.56mm sized cartridge they are defiantly not going to switch to a completely new cartridge. This cartridge would require new carbines, rifles and machine guns to be developed.

*All the photos in this blog post were taken by DocGKR at M4Carbine. You can read more about this cartridge at Cris’s blog. *

[ Many thanks to Hugh for emailing me information about this cartridge. ]

Steve Johnson

Founder and Dictator-In-Chief of TFB. A passionate gun owner, a shooting enthusiast and totally tacti-uncool. Favorite first date location: any gun range. Steve can be contacted here.


  • Maigo

    I thought assault rifle rounds where already intermediate

  • Vak

    What I don’t get :

    – Why people still think having the same cartridge for machineguns and sniper rifles makes sense. You don’t use ammunition of the same quality anyway ! It would be better to have a beefied up carabine cartridge as a “general purpose” round for all squad weapons that could even be used on DMRs (the general idea would be engagement up to 600-700 meters) and have .50 and 40mm as “defensive” weapons. Snipers would get something equivalent to .338 or .300mag and everyone will be happy.
    – While we’re at it develop a cartridge that wouldn’t need 20″ of barrel to work properly. If weapons barrel could be reduced to 14″ or even 12″ and still work well, there wouldn’t be any need anymore for short carabines used as CQB rifles.
    – Get rid of the M16 magazine platform. Seriously, it’s getting old and it’s actually a problem when you want to develop a new carabine, like the SCAR or ACR, as it is actually a really easily swappable part that causes most of the problems.

  • mikee

    Another incantation of the 7mm TCU?

  • Matt Groom

    I would think that the difference between the 7.62 NATO length cartridges and the 5.56 NATO length cartridges is not enough to justify building a new platform that could handle both. That means that this will be a 7.62 NATO platform projectile, with all the attendant capacity, size, and weight issues. The only advantage would be that you could use a 7mm VLD projectile, like the 180 grn BTHP by JLK which has an average G1 BC of .645! The downside, of course, is that it weighs 180 grains. If you only want .411 or better G1 BC, then both Berger and Hornady make 75 grn .224″ projectiles which can achieve that level of performance, and they could be made to fit into 5.56 length magazines.

    Considering how hard people are pushing for a 14.5″-16″ 5.56 launcher, I seriously doubt that any larger than traditional intermediate length cartridge will offer any advantages that will not be attended by heavy recoil, higher weight, lower capacity, and unacceptable muzzle blast. Not to mention, the platform will have to be at least an inch longer, non of the current issued equipment will work with the system, from mag pouches to storage racks, and most people can’t even shoot a 5.56 without flinching. All accuracy, range, and energy benefits are lost if the shooter closes his eyes when he pulls the trigger.

    Also, due to the way bullets are manufactured in order to be FMJ, as opposed to open tip, I think it would be very difficult to make a 130 grn projectile with a .411 G1 BC. It would probably have to be closer to 140 grains or more to get a BC like that, especially with a open base, FMJ type design.

  • Whatever

    Do the users of the 7.62x39mm cartridge show the same amount of buyer’s remorse as is shown by the users of the 5.56x45mm cartridge?

    Of the replacements for the 5.56 round, the one I thought had the most potential was the 6.8 SPC cartridge loaded with a 85 grain bullet at around 3000 fps though it’s probably not enough of a boost over the 5.56 round to justify replacing it.

  • WJS

    The return of the 7mm cartridge!! IIRC, FN initially adopted a similar 7mm caliber for the FAL before it got standardized for the .308/7.62mm NATO round

    • wjs:

      you remember correctly.

      the fn fal originally had some development with the 8×33 kurz, and then it was developed in conjunction with the .280 british.

      after the brits kicked the .280 to the curb they found the em-2 could not be satisfactorily upsized to the 7.62x51mm, so they went with the fn fal, which could be and was upsized to handle the 7.62mm cartridge.

      i can only imagine what a handy little rifle the fn fal would have been, if issued scaled to the .280 british. it’s a pity, really, that the .280 was not kept in service by the brits. a fine round.

      john jay

      • Actually, there were quite a few EM2 prototypes made in 7.62x51mm, and even one converted to .30’06.

  • G.O

    Interesting… It may not be as different as you think it needs to be. I’ve got a block of aluminum I am working on turning into a heavily modified AR-15 lower, specifically, it will allow a cartridge to have a max OAL 0.250 inches longer than the standard 5.56mm cartridge while using a 100% standard upper half to the rifle.. magazines have to be modified as well (and bolt face if you can not set the rim to the same dimensions as 223 or another commonly available AR-15 bolt), but

    • PG T

      Wondering how the Lower worked out, what bolt you used or did you create one to withstand the higher pressures..
      This would definitely put the 6.8SPC-X into play with a better seating depth to powder..

      Thanking you in advance


  • Niko

    When the M1 Garand was being developed it was originally chamberred for the .276 Pedersen before ultimately being adopted in .30-06 Springfield. The .276 Pedersen has great characterstics as a military round (good ballistics, catridge taper for easy extraction, low recoil) that could be used in all squad level weapons. Why not review this round as a potential candidate?

  • Zach

    Your final paragraph is spot-on. This looks like a nearly ideal compromise, but good luck getting any military to adopt it. That, in turn, means it would likely be scarce and very expensive on the civilian market.

    And it’s probably only a marginal improvement on 6.8 SPC, which at least has somewhat of a civilian market.

  • Redchrome

    I agree with Vak that the AR15 magazine is the worst thing hindering development of reliable small arms today. We really need a new magazine design, that incorporates the best-known features such as:

    – Reinforced magazine lips (like the Kalashnikov)
    – tapered lock-up mechanism for dimensional tolerance (like the rear locking lug on a Kalashnikov magazine)
    – straight in-out & drop-free operation (like the AR15)
    – constant curve geometry (like the Kalashnikov)
    – no-tilt follower (Kalashnikov mag followers fit tightly and ride in ‘rails’ because of the constant curve geometry)
    – bolt hold open mechanism (like the AR15)

    I don’t have enough experience to be able to say what style of mag release is best; I think there’s room for healthy disagreement there. It should be ambidextrous in any case.

    As for the 7×46; the issue I have with it is that it’s still a very straight-walled design, like most other American rifle cartridges.

    Russian designs like 7.62x54R, 7.62×39, or even 5.45×39 have heavily tapered bodies. I calculated 7.62×39 as having a 2.68 degree body taper and 5.45×39 having 1.6 degrees (please, someone correct me if I’m wrong). This is even more than a Morse taper as used on machine tools (lathe tailstocks and the like), which is ~1.5 degrees, and designed to break loose & come out easily from the socket it’s in. This means that even with steel-cased ammo, corroded cases, dirty chambers, and the like; the cartridge still inserts and extracts easily from the chamber. Also, the heavy taper means that the nose of the bullet points up from the magazine towards the breech more than a straighter cartridge like 5.56×45. All this makes feeding and extraction *far* more reliable, and is one of the many reasons why AKs are so reliable.

    American cartridges on the other hand, seem to be derived from bolt-action rifle rounds, wherein a straight body gives you more efficient use of space (and possibly easier logistics); and extraction isn’t as much of a problem since pressure has long since dropped off by the time extraction happens and you’ve got a dude who can just add a bit more force if he needs. .308 is derived from .30-06; 5.56×45 is derived from .222 Remington.

    .50 BMG and .276 Pedersen are rather an exception to that generality; both being designed right off to be used in autoloading firearms. However, .276 Pedersen wasn’t adopted in spite of all the recommendations for it. It’s interesting to note that this new 7×46 round is pretty much a ballistic duplicate of the .276 Pedersen from 1928; just in a slightly smaller case as allowed for by modern powder designs.

    In any case; a case with little taper pretty much requires a brass case, because of the self-lubricating properties of brass. With a more heavily tapered design, you can get away with the cheaper steel cases. This is why shooting steel-cased .223 in an AR15 tends to give extraction problems; yet AKs will feed & fire until the end of days with cheap steel-cased ammo.

  • Colin

    Congratulations to Mr. Murray on inventing the .280 British (7mm mk1z) from the 40’s…

    Now, if only someone would re-invent the Enfield EM-2 to put it in, then I’m on the next boat to Ellis Island (note the historical reference). πŸ˜€

  • G

    I think it’s closer to the .280 British:

  • Sounds a heck a lot of like the Brit’s .280 cartridge. I don’t like the idea that weapons chambering it are larger then other rifles that use assault rifles cartridges. I’m betting you can only fit 20 of these in a magazine. Interesting cartridge though.

  • Lance

    It might work but NO NATO brass will adopt it I think the brass has there mind set.

  • Komrad

    7mm is a good size
    big enough to punch holes but not so big as to be heavy or recoil hard
    VAK brings up a good point about sniper/machine gun compatibility

  • Mikee,

    The 7mm UIAC’s fatter parent case has more powder capacity than the 7mm TCU.

  • d

    umm the soviets got away from 7.62×39 seeing the advantages of 5.56mm by changing to the 5.45mm. Now we are going back and going to a 7mm? Going around in circles

  • Brad

    Imagine all the grief and hair pulling over the decades that could have been avoided if the original M-1 rifle had used the pre-existing .250 Savage rifle cartridge.

  • Redchrome

    the Soviets/Russians have had just as much controversy over the 5.54 vs. 7.62 debate as Americans have had over 5.56 vs. 7.62. Remember that the Soviets were very much in a ‘copying’ mindset; otherwise why would they adopt a wierd size like .22; rather than a nice round number like 6mm?

    I think you have a very good point. However, going from .30 down to .25 was probably a bit too much of an intellectual leap for a lot of the military brass at the time; who vetoed the .276 Pedersen, even tho the testing board highly recommended it.

    If the 6mm Lee had continued in use, we would have had a fine small-bore cartridge out of that, had it been given a lighter bullet and more modern powder. (it was really too far ahead of the powder technology of the time tho).

    Lots of better options have been proposed over the years; but the high intellectual inertia of government has hindered adoption of better solutions. It would be interesting to see what competing free-market armies (i.e. mercenaries) would choose, if they were of sufficient size to justify big R&D budgets. (Really, I think they’d be interested in less-lethal munitions since killing people is bad for business).

  • Vitor

    6.5mm still seems to be the magical spot to me. Twice the mass of a 5.56mm, more than enough while being rather compact and with high BC.

    The 6.8mm has a very weird shape, looks more like a nuclear ogive than a bullet that tries to be aerodynamic, it doesn’t offer any more range than the Mk262, just a bigger punch in the very same range.

  • Whatever

    Maybe this is a silly thought, but one way I thought they could make an intermediate round is by downloading the 7.62 NATO and use aluminum rather than brass cartridge cases for the lesser loads. Aluminum cases would make them lighter and make them easy to differentiate from the full power rounds.

  • Hmmm. I have a couple of rifles in a cartridge very similar to this new round: 7x47mm Mauser. We have evolved back to a cartridge size that was developed 120 years ago!

  • John

    Cool. they need to do some tests between this cartridge, the 6.5 grendel, and the 6.8 SPC. then whichever is best, build a gun for it and get it in the hands of our troops. anything other than the .223 would be a huge improvement.

  • old_guy

    “too much of a leap for a lot of military brass” re: the .276 Pederson — nothing could be further from the truth. The .276 Pederson was killed by one man, Doug MacArthur. In all of the testing the Pederson cartridge was superior especially at mid and long range and there was little to zero disagreement about that. When MacArthur killed it it had already been accepted and production had all but started. Both Springfield and Pederson had .276 rifles. Fortunately for Springfield they had privately continued development of the Garand for the .30-06 on their own nickel so they got the rifle contract instead of Pederson.

  • A few years ago, German bullet designer Lutz Moeller tried resurrecting the British .280 service round as he believed it was an ideal hunting round for medium sized game which history had not been kind to. Now, there is one more variation on the very original British idea which was pushed aside by the .308 and later the .223. If not as a service round, it would be interesting to see this old British design resurrected as a sporting and possibly target round for use in bolt action rifles. I wonder if Chris Murray has tried hunting with his new round? Lutz Moeller certainly did hunt with his 280 British round and liked it a lot. Perhaps, where military success may be elusive, success as a sporting round may be more certain . . .

    • Mehul, I didn’t know the British was used as a hunting round! Very interesting.

    • sir:

      lutz moeller was involved.

      but, the chief proponent of the .30/280 british as a hunting round has been lewis potter, a gunsmith/tradesman and firearms authority/author, who still maintains a shop in britain.

      you can obtain his email simply by googling him.

      he has sold and made rifles in the cartridge, and done some load development. oddly enough, one of the loads he sells in a blunt nosed 120 grain bullet, which reminds me of nothing more or less than ken waters final development of the 7-30 waters. (the two rounds are very similar in terms of ballistics, though nothing at all alike in case design. cat skinning, and all that.)

      i have written extensively of my version of the 280 british at http://www.wintersoldier2008.typepad.com. if leaving links like this is frowned upon, please feel free to edit the reference out.

      john jay

  • Likvid

    7,62×45 wasn’t based on 7,62×39 at all. Even when czechs started vz. 58 development (end of 1955), 7,62×39 was still virtually unknown to them (interestingly, almost same situation occured in case of 5,45×39 during Lada development in 80s).
    Jiri Cermak (vz. 58 lead designer) used 7,62×45 for early works on vz. 58 because of that (he pressumed, that both cartridges shouldn’t be much different).
    7,62×45 development was based on experience with 8mm Rapid, developed during WWII.

    • Likvid, you are right! I have updated the post. My original source was wrong.

  • Marsh

    Agree with John.

  • Redchrome

    I agree with you completely. I was glossing over a lot of things when I said that .276 Pedersen was killed by the brass… because MacArthur was ‘brass’. πŸ™‚

  • To add to Likvid’s point, the Soviets were very stingy about releasing information even to their “allies”.

    The Czech’s adopted the 7.62x45mm cartridge in 1952, so development most likely started earlier than that. There was a 7.5x45mm Czech experimental cartridge in 1948, but this used a slightly thinner case, closer to the diameter of the .30 Remington and its modern offspring, the 6.8x43mm SPC.

  • old_guy


    I’ve often wondered why intelligent people think of MacArthur as a “hero” when he was ridiculously incompetent and cost many Marine their lives in WW2 and Korea. In Korea he also slaughtered thousands of Infantry soliders — on his own side. He was the same kind of “leader” as Wilson.

    That said you made several excellent points about magazines and the Russian family of cartridges.

    I honestly think if the .276 Pederson had not been killed we would have avoided many of these discussions now about new cartridges. I think the .30 Carbine “PDW” would have been succeeded by the .22 Spitfire Johnson cartridge and we would have had both a fine battle rifle and an ultralight personal defense weapon for the past half century instead of merely making do with the option of an excessively heavy M14 or the ineffective M16 in 5.56×45. I’m not a fan of the M14 but Clinton did us no favor destroying half of them.

    My personal choice today would be:

    ultralight micro-Mauser 6.5 Grendel Spotter Rifle
    .338 Lapua Sniper Rifle together with Barrett .50BMG
    6.5 Grendel AR rifle/carbine (choose barrel length for mission)
    ultralight folding stock M2 Carbine in .22 Spitfire PDW with Goshen Hexsites

    There are few Infantry/Marine missions I can think of that cannot be handled with this array of firearms.

  • Whatever


    “I’ve often wondered why intelligent people think of MacArthur as a β€œhero” when he was ridiculously incompetent and cost many Marine their lives in WW2 and Korea. In Korea he also slaughtered thousands of Infantry soliders β€” on his own side. He was the same kind of β€œleader” as Wilson.”

    McArthur had some of the lowest casualty rates in WW2. He also was a proponent of the leap frog tactic in the Pacific, bypassing some heavily fortified islands that were not strategically important which saved many lives.

    Patton was the one who was cavalier with his troops.

  • old_guy

    Any thoughts on why the offspring of the .220 Russian and its sibling the 7.62x39mm (the family of PPC cartridges) are the most accurate cartridges ever?

    Does anyone else have any experience with the .22 Spitfire Mel Johnson wildcat of the .30 Carbine? There is also an excellent little varmint round that is also a .30 Carbine wildcat, the .19 Badger.

  • Cris Murray

    Yes, I’ve killed hogs with it, 130gr. Speer bullets. 2/3 weight of 7.62 NATO and out performs all current military cartridges used worldwide. Even beats 54R after 200 meters. I’m still a tax payer, and one cartridge is cheaper than two. Major plus is replacing the 28 lb belt fed BAR we call a M240 with a 16 lb general purpose MG, without any loss of range or lethality; PKM weighs in at 18 lbs. My 100lb wife shoots 7×46 out of my 16.5″ barreled AR10 test gun, she has no problem with the recoil.

    Answer to Goom’s question, making high BC. FMJs is easy, even the Russians can do it. The mild steel core in 54R LPS is used instead of more lead to keep CG relative to the projectile while allowing it to be lengthened without adding weight, thus improving its Length to Diameter Ratio which equals better BC. Same technique used on the final design of the 7.92x33mm 126gr. projectile.

  • Redchrome

    Thanks for weighing in Cris!

    Could you address my concerns about case taper and extraction? It would seem to me that a military cartridge should be designed for reliability first, performance second, and accuracy a distant third. Am I ignorant with my belief in heavy case body taper being good for more reliable operation, and operation with cheaper steel cases?

  • To put the case taper issue into perspective, the 7.62mm NATO has the least case taper of any issued military cartridge. When is the last time you have heard of folks complaining about chronic extraction issues with the 7.62mm NATO cartridge?

  • Redchrome

    Daniel Watters,
    If you run steel cased 7.62×51 in an AR10 I think it’s quite likely that you will have extraction problems. Steel-cased 5.56×45 is known to be problematic in AR15s; and the case taper is similar.

    We don’t usually hear of extraction problems with 7.62×51 because it’s usually brass-cased to mitigate those problems — but costs more.

    The thing that convinced me of the problems of steel cases was shooting Wolf .45 ACP in a S&W 625 revolver. Extracting 6 cases at a time (via the full-moon clip) I found I sometimes needed to push the ejector rod against something hard (because hitting that rod with my palm hard enough to get the cases out was too painful) to get them to extract. Brass cases never required more than light finger pressure to extract.

    Look at it this way. If you have two steel plates which have been pressed against each other by 25 tons of pressure (and the pressure then removed); it will be easy to separate them with a force perpendicular to them, but difficult to slide one across the other. As the angle changes from 0 degrees (horizontal sliding) to 90 degrees (prependicular) it gets progressively easier to move the plates apart; tho it really doesn’t seem to require more than a degree or two of angle from the horizontal on the force vector to make them separate easily. As the surface of the plates gets rougher (toolmarks, corrosion, dirt), the greater the angle needed to separate them easily. Now substitute ‘fired cartridge case’ for ‘steel plate’ and the analogy should be clear.

    It’s not a binary; it’s a continuum. A greater angle (more taper on the case) will be more likely to extract easily under bad conditions.

    As a rifle instructor I personally have witnessed entirely too many failures to extract when people used steel-cased .308 and .223 ammo in semi-auto guns, especially after they’ve gotten dirty. On the other hand, I’ve shot thousands of rounds of steel-cased 7.62×39 and seen many more thousands fired with *never* a failure to extract. (Only a matter of time before the odds catch up I know; but the difference is telling).

    The ammunition is one of the main reasons the Kalashnikov and Simonov (SKS) rifles are so reliable.

    There’s also the matter of feeding. A heavily tapered case points the nose of the bullet more towards the chamber as it comes from the magazine. There’s much less slamming/grinding of the shoulders of the case against chamber walls as it bounces into the chamber, so it’s feed path is smoother and more reliable.

    The downside of tapered cases of course is that they require heavily curved magazines, linked ammo doesn’t stack quite so neatly in cans, and they offer less performance for a given length and diameter because the volume is smaller. Also, they’re theoretically less accurate since there may not be as sharp a shoulder to headspace on, or a large body to consistently align on.

    Daniel, I read with interest your mention in your comprehensive timeline of the 5.56×45 (http://www.thegunzone.com/556dw-5.html) that in 1968:

    “FN experiments with a heavily tapered version of the 5.56x45mm case. The case taper resembles that of the Soviet 7.62x39mm.”

    Seems to me they were trying to solve extraction problems. I don’t suppose you have more details you can provide us on this cartridge and experiments with it, can you?

  • Regarding the heavily-tapered experimental 5.56x45mm from FN, I’ve only seen pictures of it. Solid information about the experiment and its results is scarce.

  • Cris Murray

    Redchrome, case taper and extraction failures. Case taper does lead to quicker chambering due to shape, but magazine feed lips, carrier design and bore alignment have more to do with chambering than case taper; notice how the design of the AK nearly lays the cartridge nearly inline with the bore as apposed to the AR and most Western designs that force the cartridge to exit the magazine at a very sharp angle to get to align with the chamber. Magazine design is critical to ensure reliable feeding, the magazine design for the 7x46mm UIAC is a continuous curve with horizontal reinforcing plates that have the latch slot cut in it allowing for vertical insertion and removal, similar to Hugo Schmeisser,s MP44 magazine. The US had a chance to correct the M16 magazine well and magazine when the M16A2 came out but failed to take advantage of this opportunity.

    Extraction failures are more of a cycling problem than case taper, although a steeper taper helps extraction. On a properly designed weapon system extraction should start after the breech pressure has subsided and the case has had a chance to relax away from the chamber walls. The AR system was designed to operate 650-700 RPM with a 20″ barrel, gas port pressures @18K, port 12.5″ from breech face; now shorten the barrel to 14.5″ or 16″, move the gas port to 7.75″ from the breech face, port pressure on the M4 @25K. People want a high powered rifle that cycles like a MP5 firing a low pressure pistol cartridge, this cannot be done reliabily. The M4’s placement of the gas port and higher port pressures leads to earlier opening of the breech and resulting in trying to extract a still expanded cartridge case, but because of residue bore pressure the case is nomally blown out of the chamber sometimes missing the extractor claw altogether causing a failure to eject the spent casing out of the weapon resulting in the misnomer known as a double feed when the spend case is jammed above the carrier body. The hyper carrier velocity also results in carrier bounce which causes the famous hammer down on a live round failure, because the carrier bounces back carrying the firing pin with it, away from the primer at the moment it is struck by the hammer. Bolt/carrier bounce has plagued semi and full auto weapons since their inception, Nudelman was able to design a cheap easy anti-bounce device on his NS23 cannon. The NS23 is a large gun with lots of room for extra parts.

    My test MG is a shortened rebarreled MG42/MG3. Modified feed tray and RPD links work like factory. Barrel and receiver shortened 50mm, 7×46 doesn’t need a 21″ barrel. No extraction problems with this gun or my AR10 test gun. AR15 Performance built custom bolts for the AR10

    An excellant book is Military Rifle and Machine Gun Cartridges, Jean Huon, ISBN 2-85180-122 8. This book has most of those military cartridge that people have only heard rumors of.

  • Redchrome

    Thanks for the feedback Cris. It’s great to get your input!

    I did indeed note the difference between the height of the AK feedlips and the AR feedlips, and the position of the top cartridge in the magazine relative to the bore. It’s certainly one thing among a plethora that contributes to the AKs reliability. (The more you examine and compare the AK to other rifles, you realize what a genius Kalashnikov was, and how much he optimized the design on the side of reliability).

    Jim Sullivan has pointed out in the past how the AR15 doesn’t really give the pressure enough time to drop before trying to pull the case out of the chamber. The M4 just exacerbates the problem, like you said; and the commercial AR15s with 16″ barrels and carbine-length gas systems make it even worse. It’s been pointed out by the guy who runs ar15barrels.com that you need the long barrel length between the gas port and the muzzle to function with a wide variety of ammo tho. The M1 Garand has only an inch or so between the gas port and the muzzle; but it’s picky about the pressure curve of its ammo. An ‘H’ buffer helps of course by slowing down the bolt unlocking, but of course if it gets too heavy the rifle won’t cycle.

    It pretty much needs a complete redesign of the operating system to try to cure these problems. That has been done in the case of the Robinson XCR; which is pretty much a product-improved AK mechanism. That said; I’ve seen an XCR hang up trying to extract Wolf steel-cased ammo. To its credit the rifle didn’t pull the extractor over the rim of the case; the whole bolt & carrier mechanism stayed attached to the case stuck in the chamber. A good whack with a rawhide mallet on the charging handle was needed to get the case out. This is one of the things that led me to distrust steel-cased .223 even more.

    If at all possible I think it would be a good test to try to manufacture and run some steel cased 7×46 in your machinegun. Of course, I’m sure you have enough other things to do. πŸ™‚

    As for cycling a high-powered rifle gently; there is always the example of the Ultimax 100 which runs at about 400rpm. Downside of the Ultimax of course is the weight — it’s really an LMG rather than a rifle.

    Your magazine design sounds interesting; I love the reinforced feedlips on the AK magazines. One of the often-overlooked advantages of the AK magazine tho, is the tapered locking lug in the back which offers substantial dimensional tolerance — pressing the back of the magazine up into the magwell, unlike the side-latching designs like the AR15. (Note the problems with the AR15 mags in the SA80 — Jim Sullivan said much of the problem was poor dimensional tolerance on the SA80 magwell). I have an idea for a better locking lug design, but the space here is too short to encompass it.

    Thanks much for the book suggestion. I’ll need to look into that.

    Thanks again for your comments here!

  • Dave

    Hi Mr. Murray,

    Is it still practical to have a 30 round magazine for the 7x46mm round?

  • Jake

    “Is it still practical to have a 30 round magazine for the 7Γ—46mm round?”

    Since the case base is identical with the 7.62x39mm AK round, a 30 round 7x46mm would be just as practical as the classic ak mag.

  • RNV

    Interesting cartridge although not a new development by any means. What we have here is the EM2 280 British redux. The concept is a sound one IMO and I think that were you to get SAAMI approval and a specifications it might have promise. I would love to experiment with this round a bit Chris..

  • sirs:

    some comment on historical matters.–

    1.)the fn fal was initially designed to handle the .280 british cartridge, and sized accordingly. the brits adopted the .280 british (though which dimensional version, i am not sure) along with the em2 bullpup rifle, but this decision was countermanded by winston churchill when he became prime minister again, so that britain would be in logistical step w/ the americans who were pushing the 7.62×51 for nato adoption.

    the u.s. put the twist on fn to upsize the fn fal so that it would be compatible w/ the 7.62x51mm. this fn did. only to have the u.s. then adopt the m-14 in favor of the fn fal.

    2.)the .276 pedersen and the pedersen rifle were both recommended by the ordnance dept. for adoption. and, as related above, douglas macarthur put the kibosh on that, and issued an edict that the u.s. would not make any switch in a basic infantry round with war approaching. ballistics issues aside (and, i for one, agree w/ the gentleman above who praises the pedersen round … which is tapered for extraction reason, not a virtue of the cartridge design but recognition of a weakness in the pedersen rifle), macarthur’s decision was quite sound and defensible in terms of logistics.

    and, for a comment on cartridges and ballistics.–

    1.)the 6.5/7.35 carcano’s are kicked around like bastard children, primarily because of perceived deficiencies in the design of the parent rifle. (read frank de haas on this, and decide for yourself.)

    but, look at the basic dimensions of the carcano’s, and you will note that they are very similar in almost all dimensions, except for case length, to the 7.62x39mm russian, and the 7.62x45mm, which is not surprising, since the russians were quite familiar with the carcano and used it during research. whether this had anything to do with being shot at by the 7.35mm carcano in the war w/ finnland, i have no idea, and have not seen any reference to that.

    but, the 6.5/7.35 carcano’s are also very similar in case dimension and performance to the .276 pedersen, a true .284 diameter bullet.

    2.)the 6.5mm carcano is quite similar in ballistic performance to the 6.5 grendel. most countries have found the 6.5mm insufficient in battle. it’s a fact. japan tried to change to the 7.7mm, and italy to the 7.35mm before wwii got really boiling, but decided not to because of supply and logistics problems.

    proponents of the 6.5 grendel refuse to consider this. they should.

    3.)the 7.35mm carcano is quite similar in performance to the 7.62x39mm and the 7.62x45mm in a ballistic sense, and if loaded to similar pressures would probably exceed them.

    4.)the 6.8mm rem spc is superior to the 6.5mm grendel, the 7.62x39mm russian and the 7.62x45mm czeck round at all reasonable battle field distances, say to 450 to 550 yards/meters or so.

    5.)the 6.8mm rem spc is no match for the 7.62x51mm nato in terms of energy delivery at all distances, though it is similar ballistically. the 6.8mm rem spc is a better round on the battlefield than the 6.5mm grendle, though i will concede that it has some advantages for a very long distance target round.

    6.)none of the contemporary rounds discussed can hold a candle to either the .276 pedersen or the .280 british, in all or any of its incantations, at any distance in terms of trajectory or energy delivery.

    i think the .280 british probably the better of the two, because its case design is better, but, both of these cartridges were very potent, and far easier to shoot either in semi- or full-auto mode than the 7.62x51mm nato. for those who care about such things, there is a chart in hatcher’s notebook that suggests very forcibly, that at least in comparison to the 150 grain bullet in the .308 caliber, in the .30-06 (and by inference, the 7.62 nato), that the pedersen was a better round, period.

    7.)and, for those of you who cannot get past your prejudice in such matters, i would suggest that the 7.35mm carcano/terni was a far better round than most would care to admit to.

    well, i apologize for the length of things. i am nearly 2 years behind the curve on this comment string, so i suspect no one will read it anyway, but i find the topic very interesting.

    john jay

    p.s. yes, in my view, no one has designed a round materially better in any respect than the .280 british, and a fine article on the cartridge can be found by just googling the round, and adding wiki.

    the 6.8mm rem spc is not a bad effort, but i don’t think it can lay a glove on the .280 brit.

    p.s.s. i have an upper in 5.56x45mm nato, and in 6.8mm rem spc. i use polymer mags and sierra otm bullets in the .223, and experience very few failures to feed.

    i do agree that a mag that locks from the back is a better deal than the ar-system side notches. even so, on those occasions when a round is reluctant, a little push on the back of the mag usually clears it.

    i have an article at my blog, http://wintersoldier2008.typepad.com on reliability issues with the ar-15, which center mostly on the bolt, the extractor and ejector mortise, in my view, for anyone who is interested.

    • Clarke


      I agree with most of your points but feel impelled to point out the difference between “battle rifles” and an “assault rifle” from, as you say, an historical perspective.

      Assault weapons are not intended for extreme range precision shooting. They are “intermediate power” cartridges, select fire, and generally lighter weight. The recent trend to hang everything from flashlights to auxiliary sighting systems, bipods etc onto a long arm strikes me as less than helpful to the guy in the fight. I’d rather have a weapon that weighs 6 lbs than 12 lbs. I also personally prefer a weapon that is effective at the typical range of engagement for the enemy I am facing at any given moment. If that means extreme range I sure do not want even a 7.62x51mm — give me something that will still have real punch at the end of several seconds of flight, say a .338 Lapua or .50 BMG. Personal weapons are best when they really are “small arms.” If the enemy is at 1500 yards use that most effective of small arms, a 60 mm mortar. Closer distance weapons should be labeled on their muzzles “stand still and wait for flash.”

      All the best.

      John, I’d like to discuss this and your other comment at greater length if possible. My email is clarkebw@gmail.com

      • clarke:

        today is 09.30.2012, or thereabouts. it has been a while since i have been back to this page.

        i will send an email to the above address.

        i find these topics, e.g., the “perfect” “intermediate infantry” round to be very interesting.

        another fellow who is quite into this topic can be reached at drew458@barking-moonbat.com. he is an accomplished design fellow.

        john jay

  • daniel e. watters:

    i think it probably correct that the brits tried to get the em2 to work w/ the 7.62x51mm.

    from what little i have read, little things here and there, upsizing the em2 was not very successful, nor did it function very well with the 7.62 nato.

    if i need correction, don’t hesitate.

    john jay

  • RVQ

    no one talked about the 6.5×47 Lapua, where does it stand when compared to rounds like the 6.8 SPC and 7×46 ?