First, look at the rifle. I noticed for example that in North America everything that has a short barrel and a long stock is often referred to as MS.

However, it could still be a MS. When it comes to calibers, you often experience surprises by Steyr. I own an original, non-modified MS Model GK caliber 9,3x64, a rifle that normally should not exist. It is a serial rifle, not one for a customer, but the rifle cannot be found in any catalog and Steyr does not know nowadays anything more about it either.