M1 Carbine in 8mm Kurz? The Spanish 7.92×33 CB-51 Prototype Assault Rifle

The M1 Carbine is a lightweight, handy weapon that is well-liked by many. One of its weakest points for many people, however, is its cartridge: The .30 Carbine caliber is regarded by some as being too weak to be a true intermediate caliber round fully capable of effective 300m fire. Still, the .30 Carbine is short, so maybe there is another caliber out there that could fit into an M1 Carbine’s action while giving it a little more punch… It turns out that during the late 1940s and early 1950s, at least one Spanish small arms designer felt the same way, and invented the gun in the Forgotten Weapons video below:

Ian does something a little odd in the video when he identifies the rifle as being “heavily influenced by the M1 Garand”, and continues to repeat that idea several times in the video. He’s not entirely wrong, but… To my eye the rifle looks much more obviously derived from the M1 Carbine, not the M1 (Garand) Rifle. There are a couple of clues to this: The general style of the action (mechanically similar to both rifles, but aesthetically much more M1 Carbine than Garand), the fire control group, and the mass on the operating rod. Interestingly, in lieu of the tappet gas system, the Mosqueton CB-51 uses a fixed piston with many turbulence-generating rings, that looks inspired by the StG-44.


You can see how similar the Mosqueton is to the M1 Carbine below:


Calling this rifle an M1 Carbine copy isn’t quite doing it justice, honestly (although it makes for a very snappy title). The rifle isn’t in truth a direct clone of anything, although it does seem to take more from the M1 Carbine than anything else. Besides the different gas system, the rifle features an odd grip safety, and a very German-looking front end, as well as stripper clip guides!

It’s worth noting that while this rifle is called “CB-51”, it’s not the only rifle called CB-51. It seems to me that maybe “CB-51” was the name of a trial or a program to which these different weapons were submitted, although that’s only speculation on my part.

Nathaniel F

Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. In addition to contributing to The Firearm Blog, he runs 196,800 Revolutions Per Minute, a blog devoted to modern small arms design and theory. He is also the author of the original web serial Heartblood, which is being updated and edited regularly. He can be reached via email at nathaniel.f@staff.thefirearmblog.com.


  • Joe

    Was a U.S. .30 Kurz even prototyped, or did Ordnance just ignore it and drive on with the 7.62×51?

    • They ignored it.

      • JustAHologram

        Not surprising, how long did it take for them to take note of the 6.5x55mm’s smaller bore advantages?

        • valorius

          They never did- they skipped right to the 5.56mm

          • Tom

            To be fair the 5.56mm was an off the shelf solution that was (at least in the environment at the time) superior to 7.62mm NATO. As for 7.92mm Kurtz it was a compromise round made more for ease of wartime production rather than being a great intermediate round so even had the US seen the advantage of intermediate rounds it would make sense to skip it.

          • valorius

            The 5.56mm is an intermediate round.

          • WELLS SHANE

            the 5.56 is not the better round to 7.62mm NATO .I have used both . I do not like the 300 BLACKOUT. Like the 30 better.

          • CommonSense23

            There are lots of factors that make the 5.56 a better military round than 7.62.

          • WELLS SHANE

            Have you ever shot anyone with ether round.MR STONER .Made the M16 with the 308 in mind.Have you did the ballistics. I am a vet and i have used both.The N.V.A . used auto and what you called spray tactics .There’s would go through the jungle trees our 556 would not.I would carry the M14 or the 60. Young guy’s today worry to much about weight to much.

        • .30 caliber was considered superior to smallbore stuff for a long time due to its versatility. In particular, it was felt that .30 caliber offered superior AP, API, and tracer performance.

          • JustAHologram

            And to an extent there is truth to that statement but one would think the weight savings would have some bearing.

          • That’s why they chose .30 cal and not .338. Smallest caliber that meets the requirements.

  • Reid

    So this is basically a “what-might-have-been” version of the real world’s Mini-30, practically speaking.

  • Nomar Abdiel Vazquez Vazquez

    Repeat after me: hooakin de la kalzada bayo