Welcome Razor. Your question actually labels you a newbie, only new guys sweat OALs!
OAL really ain't all that critical and YOUR rifle is the determining factor. The books OAL, or a factory round, or the crimping groove in the bullet are all ok for a starting point. It's just a starting point, not a law. You want to avoid jamming the bullet's ogives firmly into the lands but the longest limit for the OAL is usually deternined by the magazine.
The books OAL is only the length they used to develop the published data from with the rifles they used. Their rifle isn't yours, so your best OAL will usually be different. But that's an "accuracy" pursuit for later, for now all you need is some safe to use ammo that isn't ridiculusly short or long. Pick an OAL that looks right to you. Check that it will feed and chamber well, vary it until it does. Use that length to "develop" your charge.
Start low and moving up ONLY IF there are no over-pressure signs. That will take care of any variations between your rifle, OAL, cases, bullets, primers, powders, etc. and the book makers.