Good post, Kuduae - I have a couple hundred 156gr. blue nosed 6.5 bullets that mic. .2615". I bought them bulk in a bag, back in Ontario many years ago and never got around to trying them in my daughter's .260 Rem. I probably won't as I don't want gas leakage blasting past the bullets in the bottom of the grooves ion it's $400.00 barrel. They probably won't be up to that rifles 160gr., 2,550fps speeds, either.

Many of the old rifles have very deep rifing, compared to the norm today of .004" depth. An undersized bullet is held quite well and shoots amazingly well by the deep rifling.

My 9.3x57 is case in point, with it's .358 bore diameter and .370" groove diameter - .006" rifling. It shoots .365" bullets into sub 1" groups at 100 meters. As well, my M38 had .266" groove diameter, yet it shot sub 1" (4X scoped) with every bullet weight, from 100gr. to 160's and put all bullet weights into a single 2 1/2" group overall.