I have a fired brass Hispano cartridge case with the headstamp: NECO 1942 20MM M21
The marks on the rim indicate that it was probably fired in a Hispano cannon and it lacks the mark of the double-loading stop noted on some later US cases. The headstamp appears, to me, to be US and, from the shoulder height it was not fired in a British made Hispano. The crimp cannelure is a knurl, not smooth or segmented. Can anyone help with the I/D of this headstamp please?