Visual Tutorial on Delayed Blowback Operation

When it comes to rifles, most firearms owners are familiar with gas-operated rotating bolts, as it is the most prevalent type of operating mechanism being the heart of an AR-15 and AK-47 (and most other modern semi-automatic weapon systems, for that matter). Few owners are well-versed in the operation of other recoil types.

In modern firearms, one of the rarest types is delayed blowback operating mechanisms like the roller-delayed found in the MP5, CETME, etc. (even though it traces its roots to German WWII engineering efforts in both 8mm Kurz and 8mm Mauser.) Even rarer is the lever-delayed blowback system found in the French standard-issue FAMAS.  Delayed blowback, while effective, is often limiting in its band of acceptable loads (too weak will not have enough energy to full operate the mechanism and too powerful rounds will cause premature unlocking).


Given the operating systems relative rarity, I am surprised to see such an excellent tutorial on its operation. A relatively unknown and self-proclaimed “variety channel” MouseGunner has posted up the phenomenal video on the operation of delayed-blowback mechanisms.

The video makes excellent use of cut-aways of various levels to showcase how the two mechanisms work. Roller delayed blowback is showcased in a standard MP5 sub-machine gun and lever-delayed blow-back is showcased in a FAMAS rifle. The FAMAS is particularly interesting given its oddity, which the video does explain why there is the little “hump” on the back of the stock (hint, its related to ejection).



Nathan S

One of TFB’s resident Jarheads, Nathan now works within the firearms industry. A consecutive Marine rifle and pistol expert, he enjoys local 3-gun, NFA, gunsmithing, MSR’s, & high-speed gear. Nathan has traveled to over 30 countries working with US DoD & foreign MoDs.

The above post is my opinion and does not reflect the views of any company or organization.


  • Strongarm

    Delayed blowback systems based on “Momentum sharing of partial masses” begins with Hungarian Pal Dedai Kiraly and his first US patent was granted in1913 with SN.1073908. It was a “Lever Delay” construction and “Roller Delay” which developed nearly after 30 years, was also derived from it.

    This kind of mechanisms can not be explained through drawings. Sketchs, animations and other kind of visuals can only demonstrate the happenings but could not clarify why and how that delaying event occurs. However, there is a magic lifesaver term; “Mechanical Disadvantage” All explainers use it and everybody instantly capture what is going on.

    Basicaly, delaying occurs by the momentum conversation. The real breechbolt takes the momentum and transmits it to the engaged carrier through a lever with an accelarated speed and since the carrier gets more momentum than its mass deserves it becomes as if smaller than its actual mass and since total amount of momentum contains a certain amount of masses, the breechblock becomes as if bigger massed than its actual mass and slows

    Who can explain this event in drawings or animation..

  • Isaac Newton

    It wasn’t mentioned in the article (or video) but he is using the video game World of Guns. Its a very good Facebook game if you are interested the mechanics in firearms.

    • iksnilol

      You can also get it on Steam and standalone.

      I bought the lifetime access, not regretting it 😀

    • Steve

      And World of Guns is a follow-up to the iOS “Gun Disassembly” and “Gun Disassembly 2”, which were both excellent titles, and more of reference material than games when compared with World of Guns. They were also much more affordable, initially. They aren’t 100% accurate (i.e. I wouldn’t use it for reference with a C96), but most are close enough you’ll be able to detail strip and re-assemble most represented firearms.

    • Michael Rice

      Yes, a very good game. I have the Steam Version, it’s ‘free to play’, but you need to unlock weapons by earning points playing various games (field stripping, disassembly, assembly, ect) or you can just buy the lifetime pass (for what a game such as this would normally cost anyway) and have access to all the guns and future guns. Neat little educational tool, as demonstrated in the video.

  • Tony Williams

    The standard reference on automatic weapons and their mechanisms, Chinn’s five-volume work ‘The Machine Gun’, distinguishes between two different principles: those in which the bolt is mechanically locked to the breech at the instant of firing, then is unlocked by a gas-operated mechanism, the rest of the cycle being powered by blowback (e.g. WW2 Hispano cannon and some early Italian MGs), which Chinn calls “delayed blowback”; and those in which the bolt is never locked to the breech but uses some mechanism (mechanical or gas) to slow down the initial bolt opening, which Chinn calls “retarded blowback”.

    So according to him, the majority of the designs which are popularly known as “delayed blowback” should really be called “retarded blowback”. Not that anyone bothers much with the distinction these days – maybe they think “retarded” sounds rather rude!

    • Can’t we just say both are correct?
      I mean, I don’t get upset when people refer to my horseless carriage as a “car”.

    • MPWS

      My suggestion within realms of English language capability would be “transitional locking” or “semi-rigid locking” – to me they are both descriptive. Have not seen that much of former but the latter is used in different languages (mine is attempt for translation). It comes down to one thing – logical perception. What should be considered first is means, then the comes result.

  • Paul Epstein

    I was under the impression that the CZ-52 was roller locked recoil operated, not roller delayed blowback. Am I wrong on that one?

    • MPWS

      Yes you are right and what surprises me is that the knowledgeable man in reference page is not aware of it. Btw, the roller lock as applied on Vz.52 is not a suitable solution to powerful 7.62 Tokarev round. This pistol was originally conceived for 9 mm Para and there are conversion barrels for that (or used to be in past).
      It may happen, after long term use with Vz.52, that slide will give to extensive force of tiny rollers pushing into internal recesses and start to bulge. With 9mm it will cope better.

  • JumpIf NotZero

    It would be nice if he had the terminology correct.

    “This part of the bolt here” as he points to the carrier :/

  • Tony Williams

    Where does the Schwarzlose MG fit in? This had a “delayed blowback” type of mechanism in 1907.

    • Strongarm

      Though explained rather different in related documentations, Scwarzlose 1907 MG works in the same manner with Kiraly’s with a difference that, toggle lever is not connected in receiver, but on the breechblock. This lever transmits the taken momentum to the propped up recoil spring carrier as fastening and relatively lightening it, and getting excess momentum, becomes relatively more heavier and slows. In fact, if carefully resarched, it would have been seen that all mechanically delaying concepts including “Pedersen Tooge” work in the same “Momentum Converter” principle.

    • MPWS

      That is to say, solid point in sense of locking. There is however a pivot point for linkage.