.303 Brit sporter key holeing

[303tom]

Had go in the library & look this up, found it in Hatcher`s Notebook & I took this picture, it of a Savage No4.........

[runfiverun]

for odd numbers of grooves i have found that just wrapping something around the slug,and subtracting double it's thickness gives me a very close measurement to what i need.
measuring the minor [groove] measurement is more difficult and i haven't worked anything out fot it,,except a little trial and error on the nose.