My belief is that the sharp lips of the mag well and a slight lip profile difference (brand new they are usually straight or with a slight step in them) causes the shell to move too far forward before moving upwards in alignment with the bore. You did say that the brass had score marks on them - that is the mag lips grabbing hold of the shell and not allowing it to go anywhere but straight forward (and a bit up)

As I mentioned previously, the shim should be a temporary fix only and you should get to the route cause of the issue. I feel that given time (or cautious polishing) that sharp edge wears down and the round is free to move more effectively in two directions.

If you look at any mauser action the lips are "waisted" to some degree or other dependingon the usage and the shell size.

BTW - the only special marking on my BRNOs or CZ that I have seen is on the follower in my BRNO 602 9.3 x 64 where the follower is stamped "9.3x64" The mag boxes appear to be the same. However there may be differences in the newest rifles.

There is some reason that most times I prefer good used rifles - the bugs have been worked through and all the rough spots have been smoothed by time.