Alll I can say is that I must be very lucky as I have two 6.5mm Mannlichers a Mdl 1892 and a Model 1903 both of which have groove sizes of 0.268" (which appears the norm) but bore sizes of 0.256". Now I have shot the express sighted (No3 Vee) Mdl 1892 to 200 yards using some old Kynoch factory 160 Grn Loads to check the sight regulation and using handloads with a variety of bullet weights from the Speer 120 grain , Speer 140 grain and Hornady 160 Grn RN with no problems using Reloader 19.

The 1903 has a brand new Steyr made barrel and yes it's also 0.268" groove diameter. I made a brass plug guage the has 0.001" increaments from 0.255"-0.260" and both are guaged at 0.256" bores. This 1903 shows excellent promise with the 120 grain Speers.