Stoner 63A Automatic Rifle – The Original Modular Weapon

The Stoner 63 was a remarkably advanced and clever modular firearm designed by Eugene Stoner (along with Bob Fremont and Jim Sullivan) after he left Armalite. The was tested by DARPA and the uS Marine Corps in 1963, and showed significant potential – enough that the US Navy SEALs adopted it and kept it in service into the 1980s. It was a fantastic balance of weight and controllability, offering a belt-fed 5.56mm platform at less than half the weight of the M60. The other fundamental characteristic of the Stoner 63 was modularity. It was built around a single universal receiver component which could be configured into a multitude of different configurations, from carbine to medium machine gun. Today we have one of the rarer configurations, and Automatic Rifle type. In addition, today’s rifle is actually a Stoner 63A, the improved version introduced in 1966 to resolve some of the problems that had been found in the original.

Ultimately, the Stoner system was able to achieve its remarkably light weight be sacrificing durability. The weapon was engineered extremely well and was not a danger to itself (like, for example, the FG-42), but it was prone to damage when mishandled by the average grunt. This would limit its application to elite units like the SEALs, who were willing to devote the necessary care to the maintenance and operation of the guns in exchange for the excellent handling characteristics it offered.


  1. While the Stoner 63 was expensive and difficult to maintain, the Navy SEALS preferred it to the M60, just as Ian said. This is a good reminder that sometimes good performance and brute simplicity sometimes do not go hand in hand. Another example of this would be the Ross Rifle, which was prone to jam in dirt. Snipers loved it for good feeding, smooth and fast cycling, and obviously because it was accurate at longer ranges compared to the Lee-Enfield. A simple solution to the mud problem would have been a form-fitting bolt cover, which was the solution Nambu used on the Type 38 Rifle! Did I mess up?

    • Considering that, as demonstrated by Ian a few years back, the Ross rifle could be mis-assembled in such a way as to be fired without the locking lugs properly engaging, I would say that the rifle’s problems were more severe than a simple lack of a dust cover.

      • There was a safety rivet put into the Mk III variant to prevent that problem of which you speak. Ian had to remove the rivet in order to recreate the “bolt in the eye” event. So adding a bolt cover to go along with the safety rivet (and perhaps securing good quality ammunition) would have made the Ross a lot better for sniping. Another complaint was the Ross’s bayonet, which literally flew off its lug whenever one fired the Ross. That makes me wonder just who designed the bayonet lug on the Ross…

        • “would have made the Ross a lot better for sniping.”
          But would it be better enough in comparison to Lee-Enfield selected from normal production to justify having totally different weapon in inventory?

          • Let’s get this straight. The Ross was ultimately issued as a specialist weapon that shared ammunition with the Lee-Enfield. Perhaps there would be one Ross sniper for every 300 men armed with a Lee-Enfield. In this case the sniper would be set apart to target “individuals of great importance” on the other team. If the weapon wasn’t too common, the logistics would not be interrupted too much (on the premise that a specialist would NOT lose his weapon on a weekly basis). I thought about the BESA, which was a British tank machine gun that used 8×57 IS because the action could not handle .303 British. Would you rather the British tanks use the Vickers K?

          • The Ross Mk III was acquired as a standard service rifle for the Canadian Army; some 420,000 were made, though the majority ended up in British hands. It was issued as standard-issue to Canadian troops until late 1916. It’s selection was not the result of a weighed evaluation of its virtues and deficiencies, but rather flowed from the incompetence and cronyism of the then-Canadian Minister of Defense, Sam Hughes, who wished to patronize domestic Canadian industry.

            Its adoption by snipers, to the best of my knowledge, was simply the result of the fact that large quantities of an otherwise unwanted weapon were accumulating in Army stocks; it would have been relatively ease for individual snipers to get a hold of a Ross, especially after the Canadian Army began to phase it out in favor of the SMLE. Tooling and production of the Ross had been set up for large-scale production, rather than a limited run for specialists.

          • Stated simply: The Ross was superbly accurate, but ponderously long and far from “soldier proof.”

            L/Cpl Francis “Peggy” Pegahmagabow, an Ojibwe/”First Nation” soldier used one as a Canadian army sniper on the Western Front, killing something close to 400 or so Germans. So the Ross will shoot fine, if the person using it knows the weapon well, even if it wouldn’t be a “first choice.”

            After the Canadian armed forces ditched it, it was used for marksmanship training, to arm trawler crews, as military aid to UK clients, etc. In WWII, it became one of the mainstays of the LDV/ Home Guard until supplies of U.S. caliber .30 rifles and machine guns arrived after sale from the U.S., and so all of the Pattern 14 (another effective sniper’s rifle) and Rosses in .303-in. went to equip the regular army and territorials, to simplify what would otherwise have been an even more snarled up logistics problem.

    • The SEALs didn’t prefer the Stoner over the M60. We used both and liked them equally. My platoon carried 4 of each . When the M60 was modified it was fantastic.

  2. OK, so key question here that Ian didn’t answer: The Stoner 63 series is hammer-fired in the rifle configurations I’ve seen and handled, but the trigger drop on the MG systems doesn’t have a hammer, just a sear…

    So, how does that work? Is there a hammer in that top cover, or what?

    • In machine-gun configuration, the Stoner has no hammer, and fires from an open bolt. In fact there was an incident in 1968, sadly with a fatality, when a Stoner LMG in SEAL service lost one of the pull-out pins between the fire-control group and the receiver … the FCG pivoted away, and the (loaded) gun began to fire (since the sear was no longer in contact with the bolt carrier). I think Cadillac-Gage changed the pin design after that …

      • So… What takes the place of the hammer, in the MG configuration?

        With the other MG systems I’m familiar with, there is either a hammer or there is a striker; am I to take from this that the Stoner 63A has both, then?

        What, precisely, is acting upon the firing pin, in this configuration?

        • I have a reprint of the “Preliminary Operator’s and Organizational Maintenance Manual” for the belt-fed Stoner 63A. On page 33, in the instructions for assembly of the bolt, bolt carrier and piston assembly: “Replace the firing pin in the bolt carrier and pushing in on the rear of the firing pin, rotate the carrier cap assembly 1/4 turn clockwise locking the firing pin in the forward position.” Which essentially makes a fixed firing pin; the sear releases the bolt, which rushes forward, strips and feeds a round, and fires the round as soon as the bolt is up against the primer. The sear just gets out of the way, and the gun fires full-auto until it’s out of ammo, or you release the trigger.

  3. While the 63 series is a remarkably flexible firearm, Stoner’s earlier AR-15 has evolved into something even more flexible – 4 different belt-fed mechanisms, calibers from .17 HMR to .50 BMG, drums to 150 rounds, manual bolt actions, lever release, blowback, gas piston and DI locking mechanisms, and now delayed-blowback actions.

    The cleverest design in the world cannot overcome what the market chooses.

  4. Robinson armament in Utah briefly tried–and apparently failed?–to bring this to the civilian market as a self-loading rifle or carbine, with a bottom-feeding or a top-feeding “Bren style” magazine… I never found one, but my proclivity for the top=feeding system is perhaps widely known. A very interesting and truly “Forgotten Weapon.” Thanks for the appraisal, Ian!I do believe the only other example of a similar system that utilized a single receiver for a belt-fed, vehilce-mounted-belt-fed, and shoulder fired infantry arm was produced by the Czechs. Perhaps a future article might usefully compare and contrast Stoner’s 63 “multipurpose” SMG, carbine, rifle, automatic rifle/Squad Automatic, LMG, MMG with similar efforts like the British EM-2/Taden and the Czech conceptions? Also maybe this or that other system too…

    • IMHO, the compromises necessary to make these ideas work in the real world are always going to result in systems that are inferior to purpose-built designs. You can’t do everything with the same basic tool.

      Likewise, the quest for the universal cartridge; the requirements and characteristics unique to the individual weapon and squad support weapon roles militate against filling those roles with one unitary cartridge. Until, and unless the requirements for an individual weapon rise due to body armor past the point where we expect them to be capable of controllable full-auto fire, those IW cartridges we design and procure will be unable to fulfill the tactical role we expect from the medium MG cartridges.

      • “the compromises necessary to make these ideas work in the real world are always going to result in systems that are inferior to purpose-built designs”
        I agree. Notice that RPK, at first glance might looks to use same receiver as AKM, however in reality it is heavier (strengthen).

    • “do believe the only other example of a similar system that utilized a single receiver for a belt-fed, vehilce-mounted-belt-fed, and shoulder fired infantry arm was produced by the Czechs”
      While, maybe not having as many common parts as Stoner solution, efforts of Degtyaryov should not be overlook. He developed family of 3 machine guns: DP (infantry), DT (tank), DA (aviation) having much in common. Later he tried to make universal machine gun, which would become DS, but due to very strict requirements it was impossible to make it world reliably*. Nonetheless tank variant was developed and adopted as 56-П-423Т:
      unlike base model* it has (one) Rate-of-Fire equal 850…900 rpm. Co-ax (moving together with main gun), standalone (for example for T-38) and AA mount (place on top of turret) were developed. Belts proved to be much more space-efficient storage system that DT 63-round pan magazines, for example T-38 with DT carried 1512 cartridges (24 pans) when with 56-П-423Т carried 3250 cartridges.
      As addition to DP-DA-DT family RP-46 (company) might be counted, it was belt-fed variant of DP (though it still can accept DP’s 47-round pan magazine) with heavier barrel, allowing more intensive fire.

      * – there are various reasons behind reliability problem, original requirements called for machine gun not inferior to Maxim machine gun, but no more than half it weight which mean that there was need for provide ability to prolonged fire without overheating, moreover there was requirement for ability of AA fire which resulted in need of higher Rate-of-Fire, to add complication when machine gun was in advanced stage of development requirement: must be able to consume to Maxim [canvas] belts, this meant complete redesign of feed system created for metallic belts. Finally this machine gun was doomed by fact that it could work quite reasonably well with “recent production” 7.62x54R but not stockpiled older (“tsarist”) cartridges.

    • What you may have on mind is Czech designed URZ weapon system which never made it past prototype and testing stage..
      It was designed for 7.62x51mm Nato round.

      This is the closest what comes to Stoner63 as far as I know. Conspicuously, it was NOT designed for Czech military but for export. My feel is that this was part of short lived changing political climate in middle and the end of 1960s. Many other Czech industries saw opening window of opportunity and tried to take advantage of it. This came to abrupt end after WP armies invasion.

      • “(…)vehilce-mounted-belt-fed(…)”
        But, is there need to vehicle machine gun firing 5,56×45 NATO cartridge? Czechoslovak solution used “7.62x51mm Nato”, cartridge often encountered in such applications. How many 5,56×45 NATO-firing vehicle mounted machine guns were used in real combat in any significant numbers in their role?

        • Referring to current M.E.N.A set of wars I cannot recall, part of small exception (M16s given away to Kurds) did not see ANY 5.56×45 weapon. Most typically seen are AKs in 7.62×39 and PKMs in 7.62x54R. There is tons o them, all over the place.

        • Oh yes, I would like to know what lead E. Stoner to design his system in 5.56 instead of 7.62. I suspect it was trend of the day and also that time M193 was quite different than current variants. It proved deadly in Nam.

          These days the U.S.Army procurement calls for 7.62 automatic rifle. That would be field for Eugene if he still lived. I am sure he would address it.

      • Jiri Cermak and the URZ prototype. Yes, that is it. I’ll try to commit it to memory…
        So we’ve got Rossignol, France ca. 1904..,
        A nod or tip of the hat to the Luftwaffe’s Fallschirmjägergewehr 42 (arguably… I mean it was mostly to be a rifle/ light automatic rifle, not really an SMG and LMG too… Still, should be included.
        The British EM-2/TADEN project, perhaps. SMG-rifle-auto-rifle/ LMG with a belt-fed machine gun for sustained fire.
        The U.S. M14? No more SMG, no more carbine, no more BAR… Only not so much.
        Some early ideas to create the M16 based automatic rifle/squad automatic–cue USMC and the M-27 version of the HK416, perhaps?
        The Stoner 63 and Czech URZ prototypes
        The aforementioned Kalashnikov+ RPK and maybe a few others?

  5. What a great find, Ian!

    Lucky for me, that just happens to be the form of the Stoner 63 I think is most interesting. I’m only sorry I couldn’t see you shoot it too.

    (Of course, not as sorry as the fact I can not afford such a fun relic for myself!)

  6. This is a “mother” (or father if you prefer) of all shows on FW!
    The piece Ian presents is priceless showcase of designer’s genius. It clearly shows huge departure form previous AR15 design concept. In my mind this is far superior to former and lot more common sense system (stampings instead of ‘fohgings’ for one). Unfortunately designer’s motivation to create “universal weapon” proved to be its Achilles’ heel.

    With mild stretch of imagination I can see this as a true current and future system in U.S. service instead of buying overprized foreign weapon (this being M27) or elaborating on “lightweight” ammunition which poses new and unknown set of problems. Teach soldiers how to shoot and you do not need anything ‘lightweight’.

    • “Teach soldiers how to shoot and you do not need anything ‘lightweight’.”
      Wait. Do you want say that, something like around 150 years of development of metallic-cartridge firearms, to improve fire-power-to-mass ratio, was useless?
      So you would not have anything against to drag with yourself Maxim 1910, when your opponent would have, say PKM?

      “elaborating on “lightweight” ammunition which poses new and unknown set of problems”
      Wait, what new ammunition? Also it is logical to lighten ammunition, if more ammunition is delivered than weapons (in term of tons).

      • On subject on shooting skills – it is complex subject. I know from my own experience that one day on same range with same rifle I can produce at 300yrds one pattern and another day quite different one. But having said that, trigger vis-à-vis breath control are skills which can be developed.

  7. Current rifle ammunition is result of long development and is on its peak. I do not take argument it is heavy because of brass (or steel) casings; much of weight is attributable to bullet. Besides, field of development is open to aluminum (used with success in pistol ammo) and synthetic materials.

    You as person of formidable skills in ‘search and hit’ on net can easily find under title LSAT this

    • “You as person of formidable skills in ‘search and hit’ on net can easily find under title LSAT this”
      Well, when you said “new” I was thinking something absolutely new, “telescopic” (I would rather call it buried-bullet) and polymer-case combination was firstly used yet in 1960s, if not earlier (DARDICK TROUND).

    • “field of development is open to aluminum (used with success in pistol ammo) and synthetic materials”
      And regarding such materials, although in construction of machine guns (not ammunition) see here:
      photo described Ультралегкий авиационный пулемет Скотти калибра 6.5 мм из магниевого справа Электрон, it was designed for 6,5 mm (most probably Italian) cartridge and has mass of unloaded weapon no more than 4,5 kg. As description says it was made of Elektron (that is magnesium alloy), hence it mass, on other hand I think building machine gun from material used to fill incendiary bombs during Great War might pose some problems for user if it would start fire, on the other hand, at least according to Russian Wikipedia query it will start flaming if temperature is at least 600 °C.

  8. Dear Ian,
    Have you ever taken the buffer system in the bolt/carrier apart. I seems a very
    clever way of reducing the sudden shock of the piston on the cam track

  9. Der Ian, your Informations on the Bayonet are sadly wrong. Solingen is the City wäre the Blades are made (I thougt it is famous for knifes) an the Squirrel Logo is the Brand oft Eickhorn Knives, the manufacter company. so the Squirrel has nothing to do with Stoner vor the 63, its in all their Blades.

  10. Dear Ian, your Informations on the Bayonet are sadly wrong. Solingen is the City wäre the Blades are made (I thougt it is famous for knifes) an the Squirrel Logo is the Brand oft Eickhorn Knives, the manufacter company. so the Squirrel has nothing to do with Stoner vor the 63, its in all their Blades.

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