L. James Sullivan’s Rifle Patent – The MGX

In 2012, AR-15 designer Jim Sullivan applied for a patent for a new rifle design. Apparently based on his Ultimax 100 light machine gun, the rifle features a quick-change barrel, a guide-rail-less receiver with a “backbone” guide rod attached to the lower receiver, a modular trigger pack, and dual firing modes in the open and closed bolt positions.

The rifle carries over elements from many of Sullivan’s other projects:

  • The unified machine gun/rifle concept from the Stoner 63
  • The Stoner-Johnson bolt of the AR-15
  • The quick-change barrel and basic operating mechanism and construction of the Ultimax 100
  • Open bolt full auto/closed bolt semiauto operation shared with the Ultimax 100 Mk. V and later, and Sullivan’s modified M4.
  • Utilizes the Sullivan-designed Surefire 60 and 100 round magazines

In this way, it’s a quintessentially “Sullivan” design:


Image from the Sullivan rifle patent, showing the closed bolt/open bolt trigger mechanism.


There’s no doubt in my mind that the design is well thought-out; Sullivan is perhaps the most accomplished small arms designer alive today (and hopefully will continue to be for many years to come), having had a hand in several iconic and popular rifle and machine gun designs, such as the Mini-14, Stoner 63, Ultimax 100, Ruger M77, and most famously the AR-15. It would be very exciting to see this rifle enter production and – of course – I’d love to shoot it!

EDIT: Commenter mechamaster has posted a link to a prototype of this rifle (apparently called “MGX”) being test fired by Sullivan’s company Armwest. The video, embedded below, shows the weapon firing 100 rounds of 5.56mm ammunition, changing bolt and barrel assemblies, and the firing 100 rounds of 6.8mm ammunition in less than 53 seconds total:

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 is also the author of the original web serial Heartblood, which is being updated and edited regularly. He can be reached via email at nathaniel.f@staff.thefirearmblog.com.


  • BattleshipGrey

    Looks pretty wicked. Would this be designed to someday replace the IAR/M27 and/or the M249? Or would this be for when the ’86 registry gets repealed (not holding my breath)?

    • mechamaster

      For a new gun not derived from M16 / M4 / AR15 family or from existing design ( to replacing M27 or M249 ), the chance presently are… slim…

      ( Hopefully I was wrong, because I like this concept to be produced and maybe.. adopted in the military as soon as possible ^^ )

    • Joshua

      The M27IAR competition had the option of 2 open bolt rifles, they chose neither and also chose to test cookoff rates with closed bolt mode only thus both failed the cookoff requirement.

      The FNH HAMR was who I thought had it. While not a big SCAR fan, the HAMR fixed the issues of the normal SCAR rifle.

      • There is a lot of conspiracy theory thrown about that the USMC was trying to sneakily adopt a new rifle. I can say anything to that; the documents, interviews, and articles I’ve read suggest that in fact they really wanted a BAR successor, and in that context a beefed up but otherwise not particularly fancy AR-15 makes a lot of sense, versus the competition.

        There is always a possibility of something else going on behind the scenes, though.

        • Joshua

          Its tough. They did look at adopting the M27 fleet wide but found it to expensive, would require 10+years to complete and offered only a small upgrade.

          The hk416 also did not have the best cook off rate, it did however have the best barrel life at around 15,000-20,000 rounds. Others had around a 10,000 round barrel life.

          The 2 entrants that fired open bolt had the worste cookoff rates, but they were forced to test closed bolt even though technically their cokoff rate was infinite and they did not retain a round in the chamber.

          I can see why people think it was a back door attempt at a new rifle.

          The hk416 was the lightest entrant as well. The HAMR and other Colt entrants were 10-12lbs while the hk416 is 9lbs. But like I said cookoff wise others had a much better advantage.

          • LCON

            and the fact the Marines never adopted a High Capacity mag to partner it with helps little

        • BattleshipGrey

          So what aspects of a BAR were they hoping the successor to have? A 7.62×51 caliber or x63 (which I highly doubt). I suppose if they include the new 50 round drum mags the SCAR H with beefier barrel would make a good platform.

          • A magazine-fed squad-level longarm designed for sustained point automatic fire, as I recall.

          • BattleshipGrey

            Wow, they were really keeping it vague. They must really be looking to adopt anything.

          • There were more specific requirements, but yeah, I really think they were just going for a BAR successor.

    • If I understand Sullivan’s design ethos properly, he envisions an infantry rifle that can do double duty as a squad support weapon/light machine gun. So basically you’d have the carbines, rifles, IARs, and SAWs all replaced by the same gun.

      My biggest objection to this is that the weight of an M4 fully loaded is already encroaching on that of full caliber rifles like the Gewehr 98 and Garand, so it’s probably not a good idea to make components like the receiver any heavier without very good reason.

      The cost reduction from unifying those weapons, however, would undoubtedly be significant.

  • mechamaster

    Ultimax but with more AR15-ish part commonality. Nice design.

  • echelon

    I wonder how modular and ambidextrous it is?

  • blackspike2710

    No folding stock? Pass.

    • From the patent:

      “The stock can be a folding stock, a collapsible stock, and/or a removable stock. The stock can be a rigid stock that does not fold or collapse and that is not readily removable. The stock can be any desired type of stock.”

      The patent drawings appear to show a stock that can be folded either to the right or the left, depending on user preference.

  • Okay I see a front sight, and a rear sight, but what’s that labeled 113 on the top rail? Charging handle? But the charging handle looks like the round piece above the magwell…

    • Xpunge

      Barrel latch, for quick change out of the barrel.

    • J.T.

      Possibly to lock and unlock the barrel for removal.

  • mosinman

    coming to a FPS near you

  • MountainKelly

    Looks like it’d be a bear but I like the concept.

  • Armwest is Sullivan’s company. This is the design, I believe. Thank you very much for linking this, I’ll put it into the post body proper, with attribution.

    • mechamaster

      Umm, sir, in the video intro, it’s called “ArmWest MGX” as the proper name of the prototype. Found the little hint after re-watching and google it. Thank you ( and maybe you can add some information correction too ). ^^

  • Many successful rifles do not use receiver guide rails. The AR-15, M1 Garand, Steyr AUG, just to name a few.

  • David Lowrey

    Has there been a update on the lawsuit against the full ato ban? The recent one based out of Dallas. I haven’t heard anything about it since it was initially reported on in October.

  • The Real Teal’c

    Pretty good! Here’s another pic from the patent that helps.

  • The only way to make anything that is lightweight is to practice “ounce checking”. While weight is not always the most important thing, lighter is better than heavier when designing something that has to be carried by people, and one of the secrets of good design is how to design something that is both stronger and lighter.

  • The problem with integrated accessories is that they soon become obsolete. I’m also phobic about combining multiple functions into a single electronic device. If the device’s batteries die, you then lose all of the functions instead of just one.

    • I agree with you, Daniel, but they generally are a lot lighter, and that ain’t nuthin’.

  • This seems like it would play well in the IAR position.