20x139 FMK steel cartridge case


The following paragraph is taken from Tony Williams website:

"20x139 FMK

This was developed in Switzerland in the late 1930s for the FMK aircraft gun (which saw limited use) and the Flab Kan 38 AA gun, which remained in use for some time after the war. This cartridge is very similar to the postwar 20x139 cartridge for the Hispano-Suiza Hs 820, but the rim is thinner and the cases of brass."

I have a cartridge case which appears to be for this cartridge but it is a steel case with brown lacquer.

The headstamp is: 284 46 D A with a white paint stencilling: 273-46A X. The screw in primer is marked: 312-46A X DC (the D and C are overlapping each other and there is a dot inside the C. Any ideas please?


  • Normally the stamped markings show data about the shell case manufacture : “284” [lot number], “46” [two digit date] and “DA” [shell case maker’s mark ?]. Those white painted markings show data about the loaded / assembled round: “273” [lot number], “46” [two digit date] and “AX” [?]. Usually the code of the plant that assembled the round is also marked with painted letters [or numbers]. The primer screw is the type with 3-wrench holes and its markings may show: “312” [lot number], “46” [two digit date], “AX” [?] and “DC” [primer maker’s mark?]. Perhaps another collector knows more but this is all I can say. Liviu 03/09/07


Interesting - I used to have a brass case for one (and now have a solid brass drill round) but I had not heard of steel cases before. You live and learn…