Tom,
I believe it's Czechoslovak, where the crossed leter "z' was usually used to indicate "zbrojovka" by several companies, most commonly seen in rifles produced at Ceskoslovenska Zbrovoka Brno. I'll have to check further, but I seem to recall that the early Brno "z-in-a-circle" mark featured a crossed letter "Z", as in your pictures.
Regards,
John