Rick in Oregon said:I'd just tell them that the bullet dia is .172" and let them figure it out.
Better idea: Buy a barrel from a known quality maker of .17 caliber barrels such as Lilja. Never heard of a barrel maker asking for bore and groove dimensions, they're industry standard for crikey-sakes.
Agree with Rick, I am on my 2nd Lilja 1:9 twist and couldn't be happier with it