4mm Zimmerstutzen Parlor Conversion for a Mauser 1914

This Mauser pistol and 4mm conversion kit failed to sell at Rock Island on November 30, 2018.

This 4mm “Zimmerstutzen” conversion kit was patented by one Karl Weiss in 1921, and produced by the RWS company in Germany. Versions were made for several different types of pistol, but the Mauser 1914 was a particularly suitable base thanks to its very easy removed barrel. The kit consists of a new 132mm long 4mm (rifled) barrel, four .32 ACP chamber adapters, a supply of 4mm zimmerstutzen cartridges, and a manual ejection rod for removing the fired cases from the cartridge adapters. The cartridge itself is basically a stretched centerfire primer with a 7 grain lead ball seated in the end. While just as accurate as .22 rimfire at short ranges, it is much less powerful, and can be safely fire with a simply pellet trap indoors without the noise and expense of shooting full size ammunition.


  1. Zimmerstutzen or Zimmerstützen?

    ” cartridge itself is basically a stretched centerfire primer with a 7 grain lead ball seated in the end”
    It is known as 4mm M20 in Germany according to https://naboje.org/node/896 it appeared in 1921 and throws 0,47 g bullet at 190 m/s. It still produced and quite popular in Germany, there even exists guns made specifically for this cartridge, for example Perfecta mod.50 or Erma ERP 74.
    Notice that 4mm M20 is also (functionally) center-fire which mean that there is not need for altering firing pin or using tilted chamber when using conversion kit in automatic pistol for center-fire cartridges.

  2. A Zimmerstutzen fires 4 mm rimfire ammunition.
    4 mm M20 is a centerfire cartridge specifically designed for indoor pistol training and never used in Zimmerstutzen rifles. A close look at the photograph shows the very different shape of the M20, which is unlike a rimfire case.

  3. Gorgeous gun and smart way to do “harmless” indoor shooting. Only reservation I’d have is with cleaning such miniscule size bore.

    • It’s all fun and games until someone loses an eye. Naughty kids of the 70’s used to play war in the woods with metallic pellet guns, and sadly they didn’t understand what dangers they were doing until they got hit. I heard this from a coworker in the office…

      • I’ve got a pair of second cousins with three eyes between them that can tell you letting 10 year old twin brothers with BB guns go play unsupervised is a dumb idea.

  4. 4mm cartridges are still made, hey?

    With a little careful machining, A-Zoom aluminum snap caps could be made as holders for the “cartridge.”

    Might be a nice little winter project.

  5. Another good reason for the longer barrel on the conversion kit is so you don’t try to fire .32 ACP through a 4mm barrel.

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