There can also be a wide variation in bore diameters. I have seen older German guns supposedly chambered for the 9.3x72R will all sorts of dimensions. My wife has an O/U combination gun that the previous owner was so certain was a 9.3x72R (under a 16-gauge barrel) that he bought a box of RWS ammo and fired half of it through the gun. The ammo was part of the deal.
But when I got home and made some measurements I found the bore was actually .350 across the lands and .358 across the grooves, a perfect .35 caliber. Luckily, the ammo was loaded with very soft bullets and caused no problems, and the bore size makes loading for the old gun a LOT easier. But you just never know....
