Bullet comparator or COAL?

[YZ-80]

BTO or CBTO, is Cartridge Base To Ogive, using a comparator, and not measuring the Meplat or Tip of the bullet.

Yes but if you really want to take care of business, I'd use BTO.

That said, others have mentioned the variation that can be encountered using COAL. I've also seen up .007" variation in ogive profiles with "cheaper" bullets. I had a box of Hornady 87 grain Spire Points for varmints for the .25-06 that were like that. Don't see it with Bergers, that's for sure.