Chinn used this chart in 1942 (it’s in Part X in Volume 4, and can be read or downloaded at this link — warning, it’s a monster .pdf). In it, he classifies the actions of the machine guns he knew:


His choice of classifications is interesting, and he includes some designs that are not machine guns (Webley-Fosbery, Williams floating chamber). But he doesn’t include everything, if only because he drew this up some three-quarters of a century ago, and designers haven’t been idle.

What’s missing, and why?

The first thing we note is that externally powered MGs are not on the list, but then, he does define “automatic machine gun” as “A weapon capable of sustained fire with its operating energy being derived wholly from the force generated by the explosion of the propellant charge.” That’s a reasonable definition, although we’d quibble about “explosion” and perhaps substitute “combustion,” and it excludes both the then-obsolete mechanical machine guns like Gatling, Nordenfeldt and Gardner, and the then-unimagined powered gatlings of the 1950s and beyond.

The next absence is the direct impingement gas system. At the time, it either had just gone into service, or was just about to go into service, in Sweden in the Ljungman AG42, which had been in development only for about a year before its issue. Of course, the direct-impingement system is best known to us today through the Stoner AR variant, which works completely differently (having a de facto gas chamber inside the bolt carrier), and secondarily through the French MAS-49 and MAS-49/56 rifles.

What else is Chinn missing? Is there truly nothing else new under the sun in threescore years and ten?

This entry was posted in GunTech, Machine Guns, Weapons Education, Weapons Technology on by Hognose.

About Hognose

Former Special Forces 11B2S, later 18B, weapons man. (Also served in intelligence and operations jobs in SF).

13 thoughts on “Classification of Automatic Weapons Actions


“the then-unimagined powered gatlings of the 1950s and beyond.”

IIRC the U.S. Navy experimented with electric powered gatlings around the turn of the twentieth century. I’m about to head out to the woods for the weekend, so maybe another commenter can provide more info or a link on this.


I believe you’re correct. I recall reading similar, but can’t recall precisely when or where.

Of course, an externally powered gun didn’t qualify by Chinn’s definition.

Another one that wouldn’t qualify would be chain guns, almost as fun to work on as gatlings.


Roller delayed blowback(stG-45, G3) isn’t on the list, I assume since it was developed later than 1942.

Hognose Post author

Yeah, that’s a good example, what we now think of as the HK (Mauser-Werke, CETME, Dr Vorgrimler, etc.) roller-delayed blowback is one.

I’m not sure whether his delayed blowback use cases include the Kiraly system or the similar rig that showed up on the FAMAS.


1942? The linked pdf is 1955, and the chart shows the MG213; which was developed 1944/45 and never fielded in WW2. A good thing too, those were some nice shiny pieces of kit. Cammed roller locking is in Fig. 6-76 on page 371. The things I couldn’t see were the nutcracker split chamber and the funky G11 rotating chamber (vertical turret chamber?).

Thanks for the pdf, it’s beautiful. The multi-projectile round in Fig. 7-7 page 420 is intriguing (motorised multibarrel guns immediately follow)…there probably isn’t anything new under the sun, someone has thought of it before, but learning about it is gratifying.


Why is “blow-forward” labeled “Frommer” and not “Schwarzlose”? Is there a Frommer I am not aware of? (I am the sort of gun dork who owns not one, but two Stops.)

Hognose Post author

Interesting question. It sent me looking at Ed Buffaloe’s and Ian’s writing on Frommer, and even doing a Google Translate of Frommer’s wikipedia page (I read most European languages, but not Finnish, Greek, Estonian, Lithuanian or … naturally.. Hungarian). I got nothin’. I am not sure what involvement he had with Schwarzlose, if any; all of the gun designers in the Habsburg Empire seem to have worked together at one time or another. However, he did have over 100 firearms and manufacturing patents (not bad for a guy whose engineering degree was honorary).

Max Popenker

Well, I’ll start here with blasphemy: this diagram is seriously and fundamentally flawed;

why? because it mixes basic operating principles (gas pressure taken from the bore; recoil impulse of the barrel; inertia; blowback) and locking systems (toggle, cam lock, rollers etc)

IMHO, that’s two different classifications that should be applied in parallel.

He also places VG-45 (“Volkssturm”) into the “gas operated” section while in reality it operates by retarded blowback

You see, some revolver-type automatic guns used gas actions with pistons (as was the case with MG-213 or later ADEN);

Roller locking was used in both recoil- and gas-operated guns;

Same with toggle or cam locking

As for direct gas impingement, IMO mixing up MAS / Ljungman system and Stoner is not entirely correct, because in the former systems gas impinges upon “external” face of the bolt carrier and does not enter the bolt group

On the Stoner, gas is fed into insides of the bolt group to operate between the bolt and bolt carrier

Hognose Post author

OK, so let’s develop a new, better, and more inclusive chart. I’ll also note that the Gast system (which I’ve always thought of as a variant of recoil operation) that Chinn dismisses as a dead end produced a Soviet aerial gun that is still in service in many nations.

      1. Max Popenker

        I believe there are many charts like that, at least in science-minded Russian sources from Fedorov, Blagonravov and later less known authors of textbooks on the subject of firearms in general and small arms in particular. Its interesting to see how classifications evolved through the 20th century.

        I’m not an academic researcher nor a textbook writer, more an amateur small arms historian; however, right now I’m trying to do almost exactly what you suggest – to publish a set of brief, explanatory articles about various types of automatic gun actions (blowback, delayed blowback, recoil, gas, inertia, external power); once this is done, my next goal is to discuss basic locking systems usually used in automatic small arms, separately from actions mentioned beforehand.

        There will be no charts like this one above – texts and illustrations, which I hope would be useful and informative for some.

        I’m not sure when editorial staff at All4Shooters portal will commence publishing these texts, but first ones are already completed and sent out for publication.

        Hognose Post author

        Ah, we’ll keep our eyes out and link when they publish. Don’t be hesitant to nudge with a comment or an email.

Hognose Post author

Awesome find! Thanks.