Raimey,
If Sodia had a request for a 6.5x70R drilling and chose to use a barrel blank they made for a 6.5x57R instead of tooling for a special barrel, and the proof house properly marked it as having 6.8 mm grooves, there would be no obligation for the ammunition manufactures to change the bullet diameters in cartridges they loaded to be used in everyone's 6.5x60R rifles. Proof marks give information on the rifle; they give no information on ammunition. The text on the ammunition box gives information on the ammunition, it gives no information on the rifle. Obviously, it is related but it is up to the shooter make sure they are comparable. With regard to calipers, everyone reloading ammunition needs appropriate measuring instruments. If they are only shooting factory ammo loaded to accepted criteria, they need no measuring instruments at all, but then they can't shoot guns chambered for obsolete ammo. You are blessed with a nice drilling that can use bullets you don't have to make or modify. You should be happy with that; you will have enough trouble with the cases. You will still need to measure them to determine if and how much to trim them. As regards the Collath bullets: somewhere you should have the GGCA "DER WAFFENSCHMIED" special about Collath and you will find information about these bullets in the copy of their catalog that came along with it.
Mike
