If you are truly measuring OAL of the loaded cartridge, it's not that large of a deal; nor MAY it matter if measuring off the ogive.
Re-read your manuals and understand the theory of operation.
The Creedmoor is a bottleneck case, so headspace is measured from the base of the case to a point roughly mid shoulder. The tips of bullets varies in shape and length, so measuring the total cartridge OAL will always vary some. Measuring off the ogive is what you care about. Factory ammo needs to function in every conceivable gun ever chambered for Creed. That includes short magazines in an AR pattern rifle. Factory and will ALWAYS be minimum spec. You only need to know at what distance every different bullet you use, touches the lands. From touching, you need to back off, making the bullets not jammed. Everyone has magical herbs and spices for the amount of jump to the rifling.
FWIW, I have NEVER found any bullet on the planet that won't shoot with 0.0625" of jump, unless you have a crappy load to begin with.
Cheers
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