was wondering if you have any ideas about caliber minima requested by law for bison hunting in Europa ?

I was in belarus 2 years ago and was offered a wisent.

I thought I did not have the right tool but was surprised that locals are using 30 calibers of various denominations

Basically anything goes

I did not take the offer up

This cow in a mink coat (basically that's what it is, just stood there looked at us and did not even want to argue !)