Spanish 8×33 Mosqueton CB-51 Prototype (Video)

The Spanish military, like many others, was quite interested in developing a new semiautomatic or selective fire combat rifle after World War II. Franco’s political ties to Germany (combined with Spanish neutrality in the war) gave them unusually good access to German arms designs, and the Spanish experimented with several variations on the StG-44 in the late 1940s and 1950s. Of course, this would ultimately lead to the development and adoption of the roller-delayed CETME, but before that the intermediate cartridge idea was very much a subject of Spanish attention.

This particular rifle, designated Mosqueton CB-51, was one of those intermediate cartridge experiments. It retained the furniture and general appearance of a Mauser bolt action short rifle, but used a long stroke gas piston and rotating bolt in a self-loading action. Only 12 of these were made, although several other designs were also prototyped concurrently (including others also designated CB-51, confusingly).


  1. Thank you so much for your indepth article on the weapons used during the spanish civil war.

    I need help here…can a 7.62mm AK round made in China be used in another clone of the rifle such as the Bulgarian Type of the AK47


    • Probably not if you live in California, where the anti-2nd-Amendment government has determined that any mechanically-identical firearm with a different name, or that comes from a diffrent factory, or is a different color, means that it must be treated as something entirely different, and thererfore must re-submit all new paperwork, pay more fees, get “safety tested” and basically go through the entire approval process all over again.

    • While the 7.62x39mm cartridge will likely function just fine in any AK variant, I think the problem you’ll encounter are the differences in the magazines.

      • “any AK variant”

        Maybe not with Interarms (IO) rifles, which judging by numerous reports, seem to self-destruct rather quickly when firing standard ammo, and so might be much better off with some sort of reduced pressure handloads.

    • Virtually any 7.62mm x 39 cartridge of any country of origin ( including China ) will feed and function reliably in any AK variant chambered for that cartridge, unless the ammunition was defective to begin with, which is an entirely different set of circumstances.

      Generally, most AK magazines for the 7.62mm x 39 cartridge will fit the vast majority of AK variants. The very small number that don’t usually require only minor modifications such as filing down the locking tab on the magazine body in order to fit properly.

      The proxy wars of modern times continue to smolder due to a wide variety of complex political, cultural, social, historical and economic factors. The ability to sustain the fighting at a given level is certainly made more viable by access to a good supply of commonly-available arms and ammunition, and this is where standardization on either one or both is a big advantage. This factor has been clearly illustrated by several reputable analysts and historians. If you haven’t already done so, I would recommend reading “The Gun” by C.J. Chivers ( Simon & Schuster, New York 2010, ISBN 978-0-7432-7076-2 ebook ISBN 978-1-4391-9653-3 ).

  2. If a K98 a M1 Garand and a M1 carbine had a child. Another cool looking piece that I’d totally buy if they made it today.

  3. Well, well, it appears that the Spaniards were definitely onto something after playing with German toys. I know the original CETME prototypes and production batches were designed around 8×33 Kurz and even a reduced charge version of 7.62×51 NATO (called 7.62×51 CETME).

    If I recall, the Americans and the British dismissed the STG-44 as a “cheap piece of stamped metal crap” unable to endure the stresses of real combat. “It will break if dropped from a tree. It can’t punch through a wall. It can’t lie down without requiring a mini-foxhole. It’s like the M1 Carbine but heavier and cumbersome, not even able to hit a guy 400 yards away. It’s a master of NOTHING BUT TROUBLE.” And to think the Soviets decided to issue the PPSH-41 and later the AK, neither of which are intended for long range accuracy or ammunition savings…

    • I’m not sure what you’re point is. The only reason that NATO didn’t adopt an intermediate power cartridge as standard after WWII was because the US vetoed. That history is too well known so I won’t bother repeating it here.

      However, if it were not for the US insistence on 7.62x51mm, it is likely that *everyone* outside of the Warsaw Pact, including the Spanish, would have adopted the UK 7mm intermediate round, and we would probably still be using it today.

      • I think it’s because the US Army and for that matter the culture in the military had an obsession with Magnum-strength rounds. The focus was upon individual marksmanship, frugality, and cooperation with other branches of the military. “Spraying the enemy” was usually the job given to machine gunners and artillery, not regular riflemen. And remember, the main rifle-caliber firepower of the US Army and the Marine Corps was the individual rifleman! And if you were to issue an intermediate round and select-fire rifle and expect a rifleman to do his duty at the same “maximum effective range” of a full power cartridge, you’d be considered INSANE enough to be shot and left to bleed out during a training exercise! Remember that the top brass did NOT want to alter combat training to accommodate “new fangled fickle pampered poodle guns made in your garage.”

        In contrast, the Warsaw Pact countries took the lessons learned from the Eastern Front and issued weapons intended for mass conscript armies, concentrating upon massive amounts of automatic gunfire at close quarters. Thus, most of the conscripts were not given bolt-action rifles but submachine guns and eventually the AK series AFTER the Korean War. NATO didn’t find out about the AK until Vietnam, if I’m not mistaken. And you know that the M14 was no match for the AK in handiness or user friendliness.

        Did I mess up?

        • Cherndog,

          When did the .308 Winchester, (and its down-loaded cousin the 7.62x51mm NATO), become a “Magnum-strength round?” I must have missed that news release. ^__^

          “NATO didn’t find out about the AK until Vietnam” Not too surprising. The AK-47 didn’t start rolling out to troops in quantity until the mid 1950s, and by that time the Vietnam conflict was well underway. I’m sure the U.S. Ordnance folks knew about developments in the Soviet Union, but considered them to be inferior in performance to what we already had. If you need a submachine gun, grab one of the thousands of M3/M3A1s and get on with it.

        • There is this tendency in some quarters to damn US Army small arms development as hopelessly backwards and obstructionist to advancement. And they use the tribulations of post-war II rifle development as primary evidence of that indictment.

          Sure the Germans eventually fielded an Assault Rifle in significant numbers during WWII. Kudos for them.

          But I would say the some of the new small arms fielded by the U.S. Army during WWII were more radical and more important to future Infantry firepower than an assault rifle: the muzzle spigot launched rifle grenade, the shoulder fired ‘bazooka’ rocket launcher, the Kromuskit type breech recoilless rifle. And in the post-war period the US Army aggressively developed and deployed those weapons, and even bypassed the rifle grenade with the advanced lightweight 40mm hi-low pressure grenade launcher.

        • As others have said, I suspect that ordinance did not see the big deal with guns like the one in the video. They already had one, the M1 Carbine. Post war it got a full auto selector. The thing going against it was a string of stories, especially from the pacific, of shooting an enemy multiple times without the enemy taking much notice of it right away. That may have resulted in a general lack of interest in smaller rounds. Advances in powders meant the 7.62X51 could be as powerful as the standard 30 caliber cartridge used in the M1 Garand. The M1 Garand had good reports of stopping power, the 7.62X51 was smaller and lighter but hit just as hard, so why mess with what works?

          The AK was a great weapon to arm irregular troops, especially in jungle warfare–but doubt that was high on the list of priorities of US ordinance at the time. And consider that in the ongoing Afghan campaign, M14’s were taken out of storage and rushed to the field. Turns out that in open spaces the battle rifle cartridge-firing M14 does well. If there had been a war in the 1950’s, the thinking was that it would be on the plains of Europe. Granted though, the M14 would be a lot handier if the barrel were about two inches shorter and without the ridiculously long flash hider it has. Handy it is not.

          Sure, in retrospect they should have gone with the British post-war cartridge, but the logic at the time was not as irrational as one might think.

          • 7.62 NATO does perform well in Afghanistan, but we must not forget that Afghanistan is at worst a medium intensity conflict with restrictive RoEs. Under such circumstances the role of small arms becomes much more important, since you just can’t always call an artillery or air strike, or even utilize light mortars organic to the unit under more symmetric warfare scenarios. All those will suppress and disable the enemy much more effectively than any small arms fire, and usually have much more range as well. The response time of light mortars is not significantly longer than small arms.

            Another factor is that Afghanistan has a lot of “patrol warfare”, where infantry moves either of foot or with light vehicles. That is typical to modern low intensity conflicts, but very atypical for WW2 and Korea, which were the latest major conflicts in the 1950s. I doubt US planners had any crystal balls back then…

        • “(…)expect a rifleman to do his duty at the same “maximum effective range” of a full power cartridge, you’d be considered INSANE(…)”
          But notice that British Army also praised accurate rifle fire high. And also I suspect that difference between .30-06 and .280 British would be visible only on long distance, rarely occurring in real combat.

  4. it looks like someone handed a gunsmith a grainy, black-and-white picture of an M2 carbine and said “make me something like this”

  5. Looking at the bolt lockup, this looks more like those Winchester prototypes you looked at in Cody, WY than an M1 or M2 Carbine clone. And the gas system is totally different, not a tappet system. Interesting mix and match of a lot of ideas that were floating around at the time. Cool prototype!

  6. Another great video Ian. That bore cleaning piece is standard. And you did have to put three of them together to make a whole one. My 1940/41 K98K has one just like it in it.

    On another subject I went back and looked at yours and Karl’s InRange video’s on the HMG STG as well as the ones from Shot Show and the ones from the NRA summer convention. I have one pre-ordered. I’m getting mine in 7.62X39 largely because of ammunition availability vs 7.92X33.

  7. Be danged if it doesn’t have a bayonet lug! Unless I’m seeing something a helluva lot like a Mauser lug on the front. Correct that unhandy bolt control (somebody had Ian in mind when he contrived that; it works way better for a southpaw), ventilate the top handguard and make it out of plastic a la the M14 guard, chamber it in 7.62×39, rig it for a receiver sight (okay, lay on a rail for scope-lovers), and you’ve got a neat little iron that should fly off the shelves. Yes, keep the walnut furniture; you can’t argue with beauty.

  8. A Spanish Mini-14 indeed! Though perhaps a Spanish Universal M1 Carbine might be closer. Many details of that rifle seem quite excellent while others not so much. That grip safety was clearly a better idea in theory than in practice. The cost and extra weight alone would make ditching that device a good idea.

    I like the dual operating springs (shades of the late Universal Carbine!), the simple gas piston/plug, intermediate caliber, and the M1 Carbine style action bedding. Adding a charger bridge to the operating rod is very clever, but I suppose an obsolescent and expensive detail.

  9. This shows what the M1 carbine could have been if it was designed in say,7.62 x 33mm.
    I think that they did not utilise the StG magazine because of the need for the bolt face feed
    “horn” to project at least 0.220″ into the magazine for reliable feeding. This is the reason the
    conversions of the K43 (both wartime and post-war fakers) are so problematic

  10. Spanish Army experimented with German 7,92x33mm, before turning towards Dr. Voss designed cartridges.

  11. It looks mechanically sound and step above M1 carbine. If caliber is 8×33, then it is about perfect.

    One thing I do not like at any of similar creations is side-located operating rod. I see advantage in being connected with charging handle (prior to ambidextrous craze) but in general, operating system should be symmetrical in vertical plane.

    • “in general, operating system should be symmetrical in vertical plane.”
      I don’t agree. ZH-29 and Goryunov machine gun are examples of asymmetrical weapons (tilting/side) and work properly.

    • “about perfect.”

      It’s interesting that the M1/M2 Carbine’s 7.62x33mm cartridge has almost the identical energy as the last major step in “assault rifle” ballistics, the Soviet 5.45x39mm, so in a way things went kind of full-circle in military doctrinal thinking.

      I wonder if, during the .30 Carbine’s development in WWII, anyone ever thought to neck the case down to, let’s say, .22 caliber, while designing a fragmenting and/or tumbling bullet to go with it? Because if such a decision had been implimented, small-arms evolution could have potentially been set on a significantly different path for many decades to come.

      • That was the 5.7mm Johnson or MMJ,…. but we must wait until the sixties.

        The M-1 carbine was deigned as a personal defense gun for non-combatants not as a squad rifleman, so greater range was not necessary.

        • One of the interesting things about the “Spitfire”, Melvin Johnson tried to make the “conversion” argument to the Ordnance department that they could get their “modern” .22 (5.56mm) hi-velocity firearm on the cheap by converting the millions of M1/M2 Carbines to this cartridge. It didn’t quite meet the 500 yard steel helmet penetration requirement tho. ^__^

      • I am irrespective of ‘all gathered wisdom’ fan of something in range of 7 and 8mm for caliber of bullet (7.5mm Swiss or French seem to fit the case). It also gives you freedom to incorporate feature you mention.

        • Oh yes, and in reduced length casing say between 30 and 35mm. Bullet can be longer as needed for ballistic optimisation, mass of around sounds 8g about right. Do I daydream? 🙂

  12. Joaquín de la Calzada Bayo was born in 1898 and egressed from Spanish Army Artillery Academy in 1922 as lieutenant. In 1943 he entered in the newly created Ordnance Engineer Corps and was assigned to La Coruña Small Arms Factory where he developed several weapons, including the CB-64 submachine gun, forerunner of CETME C-2 SMG.

  13. Thankyou so much for your responses to my enquiries. It makes sense..most ofthe insurgencies and civil wars of the 1970s have lasted longer because of the availability of uniform calibres…particularly the combloc types.

    Any insurgency that is anchored on the use of combloc ammo is bound to last much longer.

Leave a Reply

Your email address will not be published.