Zastava handgun serial number dating?
I have three Zastava M70 .32 ACP pistols. I understand the ones being imported surplus were made 1970, their first year, to 1990. They have a six digit serial on the frame, slide and barrel. The slide serial usually has a single letter prefix and dash, the frame and barrel do not. Example, C-123456. I've looked at all the photos online and only see none, C, K, and L. I've emailed Zastava USA and the Serbian factory about serial dates, with no response at all.
They have another number hand etched inside the mag well and slide that some posters claim show month and year. I don't think so as my etched numbers are 7798, 7738, and 430. Can't get a date from that. I think those may ID the assembler, or ??
Does anyone know the specific Zastava system, or another company using the same apparent system? I'd like to at least know the year mine were made. All have a K prefix, numbers are 31****.