"Seems many Euro rifles of the day were over-bored and I don't think it was a mistake. Seems the idea then was to allow some tolerance to keep pressures down, and with deepish rifling accuracy was fine as long as bore diameter was tight enough {givng depth of rifling}."

I have an Eduard Kettner retailed Gew.88 based rifle that is chambered for the 8x57J cartridge (not 8x57Js that measures lands .303", grooves .314". Another rifle I have, a #1 Mannlicher-Haenel, has lands of .305" and grooves of .316". I've thought that these may have been made tight to boost velocity. Tight bore would boost pressure, boosted pressure would be more velocity. Just a guess on my part and I may be way off base.

Vlad