Hello stug,
In the BRNO ZKK series, we are talking here about, the magazine box, a rather simple but correctly designed stamped steel piece, has the caliber OR the group of calibers it is designed for. As an example, the ZKK 601 for the .308 Win has the left side of the magazine box marked .308 W AND .243 W. In the ZKK 600, the standard lenght action, the magazine box are marked for a group .30-06, .270 and 7x64. The 7x57 are marked as such. And in my 600 9,3x62 is only stamped 9,3x62, because the magazine box for it, has not exactly the same dimentions as the one for the.30-06 group.
So, the mark that counts is the one on the barrel, for sure.