You are correct in that it is a 7x57. To the best of my knowledge these rifles were chambered in 6.5x57, 7x57, 7x64, 8x60, and 8x57. Most of my Brnos are Model 21s, but I do have a pristine early rifle just like it that has the round-top receiver, double set triggers, butter knife bolt handle and no guild rib on the bolt. Really nice examples are hard to find without having been drilled and tapped, recoil pads added, etc.

John