20mm Headstamp


A chap has asked me to ID a 20mm Heastamp, he says it is a Hisp. But can only find reference to OeL 20mm with ACS HS but it doesn’t say what ACS stands for? the rest of the headstamp indicates it is of US manufacture. Any info appreciated.

  • @ ozziammo: The answer for you is an easy one: the maker’s mark “ACS” stands for “A.S.Campbell Co.Inc.” from Boston [MA]. This company manufactured 20mm Oerlikon “S” [20X110RB] brass shell cases “Mk2” and “Mk4” in 1942-43-44. The same company manufactured 20mm Hispano [20X110] rimless brass shell cases “M21” and “M21A1” in 1942 and 20mm Hispano [20X110] rimess steel shell cases “M21A1B1” in 1942-43. — The 20mm Oerlikon “S” and 20mm Hispano shell cases have the same length of 110mm but the rim diameters have different values: 22.1mm for the 20X110RB [Oerlikon “S”] and 24.7mm for the 20mm Hispano [20X110]. Just measure the rim diameter of the shell case and you’ll know what you have. Liviu 06/12/07

  • Actually the makers’s mark has to be “ASC”, not “ACS”. An US manufacturer of 20mm shell cases with the maker’s mark “ACS” has not existed. Liviu 06/12/07


I have the 20x110 Hispano from this manufacturere. Headstamp is: “ASC 1942 20MM M21A1”

  • I only have 2 identical fired 20mm Oerlikon “S” [20X110RB] brass shell cases headstamped “A.S.C. 1942” over “20MM-MK-2”. I don’t have any 20mm Hispano [20X110] headstamped with the “A.S.C.” mark. Liviu 06/12/07


Excellent Guys, thanks, yes it was ASC, not ACS, 20mm M21A1. Not having seen the cart myself I didn’t know whether it was Hisp or Oel, the M21A1 is a dead giveaway for the Hispano. The item is owned by a third party who knows little about cartridges! Again Thanks, Regards Peter.

  • Well, I have a 20mm Hispano [20X110] fired brass shell case with NO headstamp markings. I don’t see any way finding the maker and the country of manufacture. Liviu 06/13/07