.24 Cal. / 6mm Bottlenecked cartridge?

.24 Cal. / 6mm Bottlenecked cartridge?

Bullet is non magnetic tined FMJ 0.241" diameter.
Case length is 1.559"
Base diameter is 0.314"
Rim is 0.374"
Neck is 0.256"
Bottom of Rim to mid shoulder 0.836"

Would seem to be a 6mm wildcat based on the .25-20 Single Shot case?
Who’s the wildcat expert here these days?


Hi Joe,

It is a reproduction of the so-called 6 mm or .22 S&W experimental cartridge (long case variant) made by UMC.

Measured bullet diameter from actual examples is approx. .231-.233" (5.89-5.94 mm).




Thank you.

Pricy… https://www.engelscollectibles.com/Listing/Details/192831/6mm-SW-Experimental


I think that all known examples were found as new primed empty cases with separated bullets. This explains the variations in overall length observed in “loaded” cartridges.

The bullet removed by hand. No powder. Carbon residue inside casing. So yes, reproduction.

Thanks for all input.


Do I follow right that Joe’s item is something made to replicate an authentic example as seen in Vic’s auction (which would be assembled from components itself)? Is Joe’s item considered a “fake” ?

No head view is shown for the item from the auction. Would that case head have the heavy tooling marks as seen on the topic cartridge or would it be smooth?

Is the projectile Joe shows original or something else?

Thanks for any additional info on this one and please pardon any confusion on my part.


An original (Ive had for probably over 30 years) head which is smooth and the bullet which is CN-jacketed.

My samples of this (which i got 30 years ago in the US) looking all the same as Pete DeCoux sample shown here and none of them have toolmarks on the base. They are plain, no turnmarks for removing headstamps…
So, I dought, the one, with the toolmarks on the base is an “original”


This example I have came from a wildcatter’s collection, so I think it is safe to say it is NOT an original.