As I believe I have mentioned before a few years ago a brand new Steyr made barrel in 6.5x54MS was fitted to my Model 1903 to replace the bad re-lined barrel. The goove diameter at the muzzle best i can tell using a digital caliper is 0.268" which funnily enough is the same measurement obtained from my 1893 dated mdl 1892 in 6.5x53R. The 1903 with it's new barrel which is scoped shoots the Speer 120 grain 6.5mm (0.264") bullet quite happily despite reading articles in Gun Digest on the need for over sized bullets to get any sort of grouping in my own experience this is a non issue and actually makes me wonder at the competence of some of these writers.