Mr Bill,
Here's how I decide.
I take a case that has been sized, split the neck lengthwise with a dremmel tool and cutoff wheel down into the shoulder. Now pinch the neck whenever you need to to get the tension on the bullet high enough it won't be pulled out when you remove it from the chamber. To check the OAL to contact the lands, just insert the bullet you wish to load and leave it seated plenty long. Insert the cartridge into the chamber and close the bolt. Remove it carfully and don't let the ejector cause the receiver to put any pressure on the bullet as it's withdrawn.
I do this three times to make sure the measurement is the same each time. It will be exactly the same eack time if it is done correctly and the bullet is not pulled out some from the resistance of the rifling. I measure them with a Stoney Point comparator at the ogive and add this length to the list I use when reloading. I also take a measurement from base to the tip so I know what fits in the mag and what doesn't. Know I've got to make a decission as to what to load them at.
Some shoot great right on or into the lands, some .030" - .050" off them, and some do perfectly fine and will only shoot good with over .100" off, just something you have to find out for each bullet I've found.
What you might do to speed the process up is to do your load development starting at the length they fit in the mag, if this is short enough to begin with. After you work up to maximum load at this length, move closer a few thou and shoot a few groups. Keep doing this as you watch for increasing psi signs as you come closer up to the lands at each increment. I usually shoot three 3-5 shot groups at each increment to make a valid asessment. Just remember that your mag length will dictate the OAL if the throat proves to be longer. I single feed most of my stuff so it doesn't matter to me. Most of the time I can still close the bolt over one round in the mag with the tip just up and over the top of the mag box, but yo hhave to make sure the bolt isn't pushing down on the shoulder or your runnout will go through the roof.
You can work up to max load at mag length and then reduce the load to establish the best accuracy load first then play with seating depth afterward. I'm leaning toward the finding the most accurate seating depth with max load first at this point in my development process though. It seems I've been able to find accuracy quicker this way and at higher velocity too.
Shooting three rounds per group I can check and verify about 10 different combinations with a 100 rounds, which usually takes about three sessions at the bench and at the range. Take good notes!
If I was fire forming the 308AI I would use around 44gr of Varget and a 168-178gr A-Max seated .005" - .010" into the lands with "very" lightly lubed cases.
