I had a box of 6.5mm 160gr. RN's with long 'blue' noses (a lot of lead exposed) that I purchased in bulk many years ago. They measured .263" - so as to not develop excessive pressure in old guns. They shot well in both my 6.5x55 with a .266" groove and a .260 Rem with a .264" groove diameter.

Of course any time a bullet is grossly under size, the escaping gasses in each groove could accelerate bore wear - but one would need to fire a LOT of ammo and shoot it quickly to heat the bore excessively to cause measurable wear over only a few years use.

I'd expect with the long bearing surface on these 160gr. bullets, there would be enough movement, slugging up, if you will, to seal the bottoms of the grooves even if they were a thou or 2 undersized.