To Lonewulf; yes that works, but I prefer the tool. For one thing, projectile nose tips vary somewhat so the result is not so reliable between bullets. However the Hornady tool measures OAL length on the ogive using calibre inserts.

Best powder for the 6,5x54 M.Sch. in my carbine using 160-grn Hornady .267" (Carcano) bullets was 2,511 fps using WW 760. Ken Waters said "highest velocity with a 160grain" and that is what I found. 4 (of 5)went in 1,1/4". That may have been an outside to outside measurement, I'd have to find the original target.

In terms of lands:.2564 .2565 .2564 across three different locations on the lands.
grooves: .2681 .2680 .2678 measured by gunsmith. All measurements done in thousandths of an inch with a 0—0001” reduced anvil micrometer. Note, reduced anvil means small anvil, about 1mm. So the Hornady .267" Carcano bullets are a good fit IN THIS RIFLE.

Ray Ordorica discusses bore sizes in Handloader's Digest 15th edition. In essence, groove diameter of 6,5x54 M.Sch. rifles is typically .2666 to .268”. Greener, quoted by Ordorica, says lands .256” and grooves .268”. Bingo ! So a 4 thou over size bullet is normal in this 1928 18"/46cm barrel carbine.