Say my case length varies by .005 or so. Does that mean my CBTO will too? Or not? I want to say not, as the die is seating to the same spot (in theory) or seating depth regardless of brass length, right?

Typically not, but if you are worried about it, that's what trimmers are for.

In theory maybe, your base to ogive may change a little to none at all, but if bto doesn’t change then the amount of bullet in the case will. This in turn will change the grip on the bullet. .005 doesn’t sound like a lot but it is. The other kicker is that even bullets from the same lot will have a variance in ogive to base longer or shorter .001-.002 (which I have personally seen up to .003 variance) can exasperate the case length even more.

If you are not turning your necks and anealing. It want matter. Hasbeen

What is CBTO?

Never mind, I found out.

CBTO will remain consistent but you will have different neck tensions. Will matter if you’re at the bottom edge or top end of charge range. Get a Little Crow Gunworks trimmer for the brass you use most and a manual for the rest. As much 308 as I shoot I couldn’t imagine doing them manually.

Yep,

And is the runnout controlled?

Much bigger worries before one get's to this.

Actually variance in neck tension can and does cause variances in seating depth or CBTO. Another thing that can throw you off is if the primer pockets are not uniform you can get a misreading CBTO by having a primer sticking out a thou or 2.

What is CBTO?

Cartridge base to ogive

thank you!