How Does it Work: Operating vs Locking Systems

To properly understand how firearms work, one must first recognize the difference between two fundamental mechanical systems in them. One is the locking system, and the other is the operating system. The locking system is what keeps the breech end of the gun sealed when firing (examples include tilting bolts, rotating bolts, flapper locking, roller locking, and others). The operating system is what allows the gun to unlock once pressure is at a safe level after firing (examples include long and short gas pistons, long and short recoil, and others). Blowback firearms are somewhat of an exception to this, as they use a single mechanical system to both lock and unlock (inertia of the moving parts).


  1. “Blowback firearms are somewhat of an exception to this, as they use a single mechanical system to both lock and unlock (inertia of the moving parts).”
    In Russian terminology pure blow-back is called свободный затвор which mean free bolt, thus my standpoint is that there is not locking in such guns.
    However this causes unlock to become wrong suited for naming purpose, so I would say that: weapon belong to given category (like for example gas-operated) depending on that how moving parts are put in motion.

    • Linguistics are bit fuzzy when comes to firearms. It looks Russian terminology is not exception. As far as I know, French might be further in accuracy, but than you have term such as “culasse” used for action, which also means “cylinder head”. In any case, it does not say if the mechanism is of closed or closed&locked type.

      Its a mess 🙂

      • “Linguistics are bit fuzzy when comes to firearms. It looks Russian terminology is not exception”
        At which point?

          • No, not really. It opposes cartridge pressure by its mass backed by return spring force. Not as free as it seems.

          • “No, not really”
            Ok, now I check how it is described in Fyodorov classification and he doesn’t use “free bolt” but actually Bolt recoil. Systems with fixed barrel, working [thanks to] direct pressure of powder gases at bolt these contain both pure blow-back and delayed blow-back.

  2. We haven’t covered externally powered weapons yet, like the chain gun or the Gatling. How are those kept from doing out-of-battery discharges?

    • On Gatling guns, each barrel/bolt has a separate locking mechanism, similar to conventional firearms. The operating system is driven by an external power source which turns the barrels and performs one segment of the feed-lock-fire-unlock-extract process on each barrel. with a chain gun, there’s a single barrel with a conventional locking mechanism, but the operation is driven by an externally powered chain that performs the f-l-f-u-e process.
      Ian has videos on the GE M134 mini-gun (which I haven’t yet re-watched to refresh my memory). He should get back with it’s owner & do an episode in this series on externally powered weapons.

  3. Locking works within a few milimeters from the breech, whereas operating works as following this stage and continueing in a gap measuring longer than the cartridge used, in dicharging and in opposite sequence in loading.

    ln blowback operation, the inertia of bolt mass might be accepted as locking.

    • “ln blowback operation, the inertia of bolt mass might be accepted as locking.”

      In all due respect, I’d rather say “resisting”. Czech terminology uses expression “dynamic lock” (in equivalent sense). This may be closer, but still, not accurate enough.

  4. Ian makes a reasonable statement attempting to separate both terms/ functions (operating and locking). But imagine if you described a system as “gas operated”, would you assume it is blowback? Probably not.

    It may be roller bolt head locking, tilt bolt locking (front, rear or side) or rotary bolt locking. So, first comes “gas operated” and then the rest. After that it may start to make sense.

    • “So, first comes “gas operated” and then the rest. After that it may start to make sense.”
      At least in that regard Russian terminology is superior as there is отвод пороховых газов literally bleeding of powder gases implying that [part] of powder gases is taken away from barrel [through gas port].
      Confusion arises from that gas operated meaning is somewhat more narrow, than logically thinking (as all “self-actuating” actually harness expansion of powder gases to eject case of current cartridge and load fresh one).

      • With accepted convention, message can be conveyed to mutual understanding. Since I worked in industry, I can give you example of it.

        Say you have a part which in plain language is “Trigger housing holding bracket”. If you were to write this description into title block of production drawing it will look as follows: “Bracket, Holding, Trigger housing”(item’s name, its function and where it fits). It is in reversed order as you say it; kind of French actually. This is North American convention (in Mexico it will be same but in Spanish). Every single person from management to shop-floor worker will understand it. Personally, I like it that way.

        • Another example, away from guns:
          “Chaussettes Noires Confortables” (comfortable black socks)
          you see the similarity 🙂

      • If I should use this nomenclature for whole rifle, in may sound like this: “Rifle, gas operated, rotary bolt”. Part of title may be caliber, if so desired; it would be likely at start.

    • Of course, then you run into such systems as the VG1-5 carbine and the later Steyr GB-80 pistol, which are gas-retarded blowbacks, firing from closed bolts or slides.

      In that case, the gas takeoff acts to prevent the breech from opening for a short time (milliseconds), rather than actuating the breech opening sequence.

      Are they “gas-operated”, or are they purely a variety of blowback?

      As the old saying goes, “you pays your money and you takes your choice”.



      • Conclusion is that not matter how sophisticated classification you create, someone sooner or latter would make something breaking it. Unless you add special category “anything not belonging to any other category”.

      • What is the lead phenomenon here? Gas. So it is gas operated. Further descriptor is “gas delayed”.

        Apology to all for taking too much space…. but subject is so catchy 🙂

      • The Steyr GB, has the more accurate and descriptive name
        Gas Bresme

        Gas braked

        The gas acts for a few milliseconds as a stiff recoil / buffer spring to slow and buffer the slide in the later parts of its travel –

        Without requiring the unpleasantly stiff recoil springs that you find in other 9x19mm blowback pistols. For example the square section wire springs of the big Campo Giro inspired Astra blowback pistols.

        The ultra shitty Rogack copy of the Steyr GB was effectively plain blowback as the huge clearances prevented any gas braking. It sort of demonstrated that the slide alone is heavy enough to safely fire as a plain blowback

        In practice, and H&K P7 slide is heavy enough to safely fire as plain blowback as well.

        It’s a while since I had a good look at a Steyr GB. I need to check where the gas ports are drilled. Iirc, they’re quite a way infront of the chamber, which suggests that their purpose is not to delay the initial movement of the slide.

        • The GB gas takeoffs are just behind the muzzle, allowing gas to blow into the “cup” that forms the front end of the slide and barrel bushing, ahead of the concentric recoil spring. The purpose is to prevent the slide from opening until chamber pressure has dropped to a safe level for extraction and ejection.

          In other words, it works exactly like the VG1-5 carbine.



          • Hi Eon,
            Just behind the muzzle is exactly wrong place to delay opening.
            Max pressure and max acceleration of both bullet and the slide occur just in front of the chamber.

            It’s a gas buffer.

            The days of legal, privately held Steyr GB’S in the EUSSR might be numbered, but I intend to get a good first hand look at one soon.

    Recently I become aware about MPX COPPERHEAD: sub-machi… Ultra–Compact 9mm Personal Defense Weapon (“short gun with long name” is what appeared in my mind after reading that), which is, quite surprisingly for me gas-operated, following data are known:
    Total length: 14.5 inches
    Barrel length: 3.5 inches
    Barrel twist: 1:10 ”
    Weight: 4.5 lbs
    Finish: Cerakote E190
    Cartridge: 9×19 mm Parabellum
    As it has built-in muzzle-brake I am quite confusing: is barrel length given including or not muzzle brake? What is length or rifled part of barrel then? Why so short barrel was used? Anyway, while looking at total length provided it certainly could be called compact, but after taking in account barrel length and comparing it with other, lets call it “short sub-machine guns” it does not look as great as advertised, just look:
    MP5K: 115 mm barrel, 325 mm o/a length, 2,0 kg mass [longer barrel and smaller o/a length and lighter]
    PP-2011: 120 mm barrel, 314 mm o/a length, 1,7 kg mass [longer barrel and smaller o/a length and lighter] data from
    Samopal vz. 68: 115 mm barrel, 305 mm o/a length, 2,03 kg mass [longer barrel and smaller o/a length, virtually equal mass] data from
    Sterling Mk VII: 4″ barrel, 14.8″ o/a length, 88 oz mass
    All lengths are for stock folded, excluding Sterling Mk VII which lacks folding stock

  6. The whole area of firearms terminology in the English language is a freakin’ minefield.

    I would suggest that it would be better to phrase this not as “system”, when it comes to describing things that we currently describe as “recoil-operated system” and “gas-operated system”. The problem is that we’re using the same word, system, to describe two very different things, the principle used to operate the weapon, and the means by which that operation happens. Instead of saying that the AK is a “gas-operated rotary bolt system”, I think the distinction needs to be made that the AK is actually more properly a “rotary bolt system using the gas actuation principle”.

    Of course, this is pissing into the wind, as nobody is going to pay attention to it. Within a generation, clips are going to be interchangeable with magazines, and nobody but a few fussy technical types will care that there was ever a distinction.

      • Mine field? Sounds like the difference between dummy rounds and live training rounds for aircraft cannons. One accident happened when an “inert” cartridge was loaded into a demonstration flak cannon laid upon a table. By inert, the armory guys meant “live cartridge with an empty projectile,” not “non-firing dummy.” The salesman showing the customer how the gun worked hit the trigger, setting off the loaded shell and causing the whole gun to jump off the table. The salesman suffered a lethal blow as his vital organs were crushed by the gun. I hope nobody else gets this Darwin Award.

        • That’s the kind of thing I used to rail about, while I was on active duty. Imprecision in language is deadly, as is communication via meta-data; classic example from the Korean War was this one:

          “But such an effort would endanger the entire line and relief never came. A debate rages to this day over whether the Glosters could have been pulled out or relieved sooner. Cultural differences were a factor in the confusion.

          On Tuesday afternoon, an American, Maj-Gen Robert H Soule, asked the British brigadier, Thomas Brodie: “How are the Glosters doing?”

          The brigadier, schooled in British understatement, replied: “A bit sticky, things are pretty sticky down there.” To American ears, this did not sound too desperate.

          Both sides of that conversation were at fault; the American one for not clearly and formally asking for a report, and the British for ambiguously responding and expecting someone from another culture to get the meta- parts of what they were saying.

          Confucius’s 13th Analect has implications here; clear, unambiguous communication is essential, and requires proper and correct terminology.

          • Excellent passing of experience!
            (and this fits excellently to what I know already)

            Now, let’s look at it little closer. You are talking about ‘inaccuracies’ in interpretation between you and British. How would it look, if you (such in case of taking on a hypothetical evil empire somewhere) had to communicate with say Baltic commanders. Or someone so heavily accented like myself. Just wondering… 🙂

          • “Korean War”
            According to
            In 1950, the radio code word for 60 MM mortar ammunition was, “Tootsie Roll.” To prevent the enemy from learning that ammunition was running low, American troops battling in the Chosin Reservoir in North Korea would radio, “We need more Tootsie Rolls.” One such transmission was translated verbatim by the radioman at the airstrip. When the next airdrop was made, parachute packs floated down with – Tootsie Rolls.
            Though in this case it was blessing as Tootsie Roll Industries has received numerous testimonials of how Tootsie Rolls have actually helped save the lives of service personnel who were near starvation.

          • ” How would it look, if you (such in case of taking on a hypothetical evil empire somewhere) had to communicate with say Baltic commanders. Or someone so heavily accented like myself. Just wondering”
            At end of 19th century in Europe existed state known as Austria-Hungary, also known unofficially as dual monarchy, however in reality much more than 2 nations lived inside it. Deutsch was official language for one part and Magyar for other, but mentioned nations have own languages. This presented problem as military service needed clear way of communication. For solving that problem about 80 IIRC commands in Deutsch were chosen and teach to soldiers regardless of their nationality.

          • “Both sides of that conversation were at fault; the American one for not clearly and formally asking for a report, and the British for ambiguously responding”
            There is also problem of unaware knowledge which once leaded to
            And still cause pain for anyone having to juggle DD-MM-YYYY and MM-DD-YYYY date formats (it is day-month-year or month-day-year?) – after all there is difference between 12 January and 1 December.

          • Imprecision of language often reflects imprecision of thought. I just heard a radio ad for the Babble language-learning app, in which the announcer said that its popularity in Europe was the reason Europeans spoke more languages than most Americans.


            Europeans speak more languages because for centuries, Europe has been divided into countries about the size of American states, each with its own distinct culture and language. Multi-lingual ability is vital in Europe if you go more than about 200 kilometers in any direction from any given point. It’s been that way for over two millennia and isn’t going to change any time soon, no matter what the EU gnomes in Brussels think.

            In the United States, you can get by perfectly well with English across the entire continent. Except at certain groceries and restaurants.



          • @Daweo… yet again
            subject matter: “how would it look…”

            Perfect, spot on example. What has to be born on mind (and I know that you know, but others don’t) is that dze Dzerman (or Magyar in respective areas) were historically ingrained languages in those areas. They were of second nature to local people for generations.

            In contrast, Engrich (as some Chinese call it) was imposed on people of central and eastern Europe very recently by virtue of political and corporate take-over. This new “lingua franca” is not natural to them. They still struggle with it (you say one thing and write something completely different), but they try their best. Results are bit funny, but so what.

    • I agree that word “system” is overused. It is just unnecessary pilling up words, which makes name look more fancy. If there were say 20 parts involved, it maybe justified, but hardly with 2-3 bits in whole assembly. It is along same line as whoever is involved with some technical work is called “engineer”. People do not know true meaning of words.

  7. One of my favorite aspects of Forgotten Weapons is the whole “archival for the sake of posterity” principle.
    Because, Kirk, if you are right, within a generation or so all of the depth and breadth of this knowledge will be just myth, mystery, and legend. Especially once the collections have dried up. Once all the old examples of various pistol and rifle designs are gone, the only repository for information on them will be archives like this platform.

    All the more important to record history while we still have the opportunity to do so.

    So, beyond the entertainment value of FW / InRange, beyond the gun geek breakdowns of semantic arguments, beyond the fun debates of various iterations of Mausers, etc., there lies a greater value in just the simple fact that the genius (and failures) of the past designers will be able to be preserved to stand as a beacon of light to future generations of aspiring firearms enthusiasts and creators…

    There is enormous worth in the work that is being done here, just for the sake of historical education alone. Thank you, Ian and Karl.

  8. i really like these videos. not very many people actually cover the basics of operation mechanics. Keep’em coming!

  9. Continuing on the theme of imprecise language.

    George Orwell / Eric Arthur Blair, wrote an essay titled “politics and the English language”

    In it, he point out that politics all too often (?always) misuses language to confuse, mislead and obfuscate, rather than to communicate, inform and clarify.

    The meaning of words becomes blurred and confused (my own example: the word “liberal” derived from “liber” meaning “free”.
    In present day America “liberal” now means the exact opposite, it means a supporter after an all powerful cradle to grave state)

    In Orwell’s 1984 (100 years on from the Fabian socialists’ manifesto of 1884, which stated; “even of it takes 100 years…”) newspeak was intended to make thought crime impossible

    If the concepts couldn’t be put into words, people would not be able to form them in their thoughts either.

    • The central state is not the only oppressor – ask all the people ever lynched by ordinary villagers for being the wrong color or religion, or destroyed by rich men for interfering with their profit or by a local (“limited”) government bought by those rich men. All of which was the American experience as the meaning of “liberal” changed. Under the staggering inequalities of the Gilded Age and its attendant financial crashes, liberty came to appear as a sick joke.

  10. In most countries and states no one will make his own army or he will buy big quantities of ammo, so what for the evaluations ? The books don’t make it to many countries, and if you don’t search personally in the pages it will come out as a lost affair…I have personal experience through mail orders ! Some times they never even arrived, but i had already paid !
    Finally, the show is called FW. Right ?
    Comments is not a forum !

  11. In fact, excepting “Long Recoil and Long Stroke gas piston”, the working systems of most of the firearms which carrying out; Cocking, ejecting and reloading functions occur in “Blowback Operation” which happening only the use of gained momentum and remained gas within the barrel against to the bolt mass.

    Then it might be said;

    – Locking Systems refer the way of mechanical fastening of bolt and barrel,

    – Operating Systems refer the source of power obtained to separate the bolt from barrel.

    – Working system refers the power to actuate the bolt to cock, for ejection and for reloading which happening in pure blowback…


    • That’s good way of looking at it. As you say:
      – first refers to method of connection
      – second to method of disconnection… sounds logical to me.

      And please don’t be so ‘humble’, will ya 🙂

  12. The AK and the MP44 work normally without the extractor (the M16 does not) so they could be said to be gas unlocked and blowback operated. I have a tentative theory that successful designs do not put any strain on the extractor. This could explain why the M16 case rim is prone to tear rims

    • So is the Ruger Mini-14, with its M1 Carbine type short-stroke gas-piston system. As much as I personally dislike the AR-15 system (too powder-sensitive for my tastes), the case head tear-through/separation problem is endemic to 5.56 x 45mm weapons, period. I believe the problem isn’t so much the “operating system” or the extraction system as it is the inherent faults of the 5.56 cartridge itself.

      Such malfunctions rarely happen in 7.62 x 51mm examples such as the AR-10 or etc. And they are almost unknown in the CETME/HK91 type 7.62 NATO rifles and LMGs, which are notorious for the abuse they inflict on cartridge cases.

      I’m not sure I’d want an HK type in 5.56mm. Of course, I’m not a big fan of HK other than the original CETME type in 7.62 NATO, anyway. As 7.62 x 51mm rifles go, it’s probably the least worst of a fairly undistinguished lot.

      (Expecting explosions in 3,2,1…)



        • The HK33 did not do very well in tests (concretely in Spain) afaik. There was the least of sales success with them for H&K.
          For example, one of nations who initially adopted them was Norway, who replaced them lately for C7 rifles made in Canada.

          I somehow agree with Eon that rifles in 5.56 based on retarded blowback are the least favorable option.

    • When assessing M16 “rim-reaper” affair, please keep in mind that when it made combat debut during Second Indochina War, it was supplied with cartridge which DO NOT passed all QUALITY CONTROL tests, they were supposed. According to (page 59 of PDF):
      Cartridge Case
      Initial Military Specifications
      The initial military specifications published by the U.S. Air Force were developed primarily from the commercial specifications prepared by Remington Arms, Inc., and did not provide for metallurgical control of cartridge case hardness which has been a mandatory requirement for the 7.62mm North Atlantic Treaty Organization (NATO) cartridge.

    • I have seen a study which said that extraction force on M16 may vary between 0 and 160 lbf. There were all known variables considered minus damage, fouling due to neglect and wear.

      • When I say “wear” I meant an excessive wear. The best working rifles are those which are just ‘broken-in'(fuzzy English at it again).

  13. The 5.56 has the problem of being loaded up to 65k psi.

    It actually had too small a case capacity to achieve the ballistics that the bureaucrats wanted, at more reasonable pressure levels.

    The experimental case that Remington later commercialised as the .222 magnum, had sufficient case capacity to provide the ballistics that the bureaucrats wanted, but at lower peak pressure.

    The availability of cheap surplus military 5.56 ammunition with approximately the same performance as the .222 mag resulted in its eventual disappearance from the commercial market.

    Unfortunately we have a legacy of guns built to fit the 5.56, and with the desire for carbine length barrels and further increases in ballistics, the pressure problem can only get worse.

    One possible way to lessen the extraction issue would be to thicken the rim of the case, but this would require thickening the case head web and reducing the case capacity as well as altering the existing guns.

    So if the same ballistic performance was required, pressure would need to be increased further…

    Damned bureaucrats!

Leave a Reply

Your email address will not be published.