Two Interviews With The Designer Of The AR-15, L. James Sullivan

InRange has an excellent interview (and range video!) with Jim Sullivan, a designer of the AR-15, Ultimax 100, Mini-14, and other firearms. In it, they get to fire Sullivan’s improved M4, which is more tolerant of sustained fire and employs the “constant recoil” principle used in Sullivan’s Ultimax 100 machine gun. I’ve fired the latter weapon, and I can say without a doubt that Sullivan means what he says when talking about its performance and soft-shooting characteristics. To help illustrate this, here’s a video of my friend Arthur firing the Ultimax 100 taken by a high speed camera at about 1,000 frames per second (due to the lighting conditions that evening, the quality is not as high as I would like, but the effect of the constant recoil mechanism is very evident):

In March of 2008, Small Arms Review published another interview with Jim Sullivan, which carries more detail about his time working at Armalite, Ruger, and in Singapore. Parts I, II, and III are available on the SAR website.

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



    • Yellow Devil


      • Grindstone50k


  • My main worry about Sullivan’s redesign is that the extra bolt travel and mass will end up beating up the bolt catch and its recess in the receiver.

    • Something tells me he won’t overlook that, lol.

      • Joshua

        He overlooked the fact that no one uses auto anymore. Everyone runs fast in semi and this will do nothing for that.

        • He is chasing guns like the M27 or Colt LMG, while combining the positive aspects of these firearms with those of a standard infantry rifle. He knows more than you.

          • Joshua

            So sorry for criticising him with my experiences. The BAR concept is stupid as is the Colt LMG.

            Also the M27 IAR should not have won, but don’t get me started on how they set it up for the HK to win.

          • You’re right bro, squad automatic weapons are totally lame and pointless!

          • Joshua

            The M240 and M249 are awesome, a M4A1 used as a SAW is not(which is what the M27(16″ HK416 basically is).

            I cannot believe you really just called a carbine that is fed from 30rnd box magazines a squad automatic weapon. You have no idea what you are talking about.

          • So my select-fire rpk-74 is not a squad automatic? Machine guns of my forte son, feel free to cut your losses and bail.

          • Andrew Hobby

            Oh boy…. *grabs popcorn*

        • Tassiebush

          I’d have thought the constant recoil modification would smooth out the fast semi auto fire too.

    • Tassiebush

      I think the idea with constant recoil is that the bolt never comes to a sudden stop hitting a buffer or anything else (like bolt catch and reciever) but rather comes to a slower stop against spring resistance before then going forward again and that greatly improves the controllability.

      • I’m talking about the bolt catch that engages the magazine follower after the last round is fired.

        • Tassiebush

          Ah! I see what you mean! It’d be more forcefull on it. I guess it’d need to be explored whether the existing one was up to the extra load.

  • Joshua

    No one runs around blasting away at 600rpm or 850rpm, dumping their mags at hills amymore.

    Hell no one smart ever did, Sullivan lives in cookoo land where the AR standards for assault rifle because you assault their position(yeah he said this a few years back).

    It might be a fun system, but we had controleable auto in the Mk16 and no one used it, the selector never left semi aside from range fun.

    As to carrier bounce it was fixed with the H2 buffer, and he also clearly does not realize that the hammer does not follow the carrier as it closes, it is held in place until the carrier trips the sear just when it is fully locked in battery.

  • Tassiebush

    Another cool thing in the video (the interview one) is the 100round mag. I’m curious about how the follower works on a mag like that where it is so much wider in the bottom section than the top? It looks so much handier than a drum mag.

  • Mack

    Great video, but i got a quick question hoping someone can clear up. Is it more controllable because of Sullivan new system or because of the increased weight causing lower cyclic rate? wouldn’t the same thing be achieved by H buffer with a heavier carrier? Or is that basically what Sullivan did?

    • Matt L.

      The increased weight is part of the equation, but Sullivan has also engineered this new AR to have its bolt completely stopped and reversed by the buffer spring before it actually strikes the buffer itself… that means the recoil force is transmitted to the shooter as more of a curve than a sharp spike, greatly aiding full-auto handling. The Ultimax U-100, also partially designed by Sullivan, employs the same concept.

      • Mack

        So basically there is no sudden stops, i wonder if sullivan same concept could be used with a cyclic rate around 700+? Or closer to the cyclic rate of a M4 now.

        • Matt L.

          Who knows? Of course, I really don’t see why I’d need to throw more than nine rounds downrange every second anyways. But that’s just me.

    • It is controllable because Sullivan has carefully balanced the weight of the components, stiffness of the spring, and other factors to allow for operation approaching his constant-recoil design.

      So, sort of “all of the above”, but done so that it conforms to the equation he invented governing this. Low cyclic rate alone would not be enough.

      • Mack

        Thanks, exactly what i was wondering, so even if you took an AR down to the sub 600 fire rate, it would still recoil more then his new improved AR, correct?

        • The total force of recoil would be the same, but it would be delivered not as a constant or near-constant force to the shoulder but in sharp shoves. Imagine someone leaning on you versus someone shoving you repeatedly.

  • Tassiebush

    Cheers for that Roguetechie! That patent is a great read. I agree about the importance of accepting innovations and they need to be tested. I can recall reading an author from 1860s who showed many good insights but who expressed concern at the unnecessary complexity of extractors in centrefire guns vs the proven reliability of pinfire guns which didn’t need them. Imagine if that scepticism was never overcome! Each war involves different challenges and i think automatic fire was probably far more needed in Vietnam or Borneo than Afghanistan or Iraq. Doubless it’s time will come again. The best weapons will do the most things well. Mr Sullivan is working hard at making that weapon.