The Serbs (Yugoslavs for a while) were committed to the 7.92x57 round by the early 1920's (1924 contracts and Kragujevac products) and purchased at least their first batch of VZ24's from Czech military stores so they would have been 7.92. Only Spain in Europe held onto the 7x57 into WWII and they switched to 7.92 with the Model 1943 rifles. The rust on the 7mm's certainly has a humid tropical look to it (Central or South America). Given the booming milsurp market in the US right now, I'll bet buyers are everywhere- looking for an undisturbed cache of rifles set aside when countries made their pick of sugar daddies in the Cold War.