Phorwath and MikeCR please help me understand this correctly. Your discussion appears to boil down to whether optimum seating depth or powder weight should be determined first. If these two factors are independent in their influence on accuracy, which MikeCR appears to assert, does it matter which variable is optimized first?

What do you think about testing this independence theory by using both approaches with the same rifle while maintaining all other variables, including the environment, as close to the same as possible? If these variables are truly independent, should each method result in the essentially the same final seating depth and powder weight combination? It is possible that there are local minimums in this system that could result in misleading results depending on the starting settings for each variable. It may therefore be necessary to run this test with several initial depth/weight combinations to verify independence.

Whitesheep, I think you're all over it.
I'm really suggesting that by up front picking a 'standard' seating depth(without basis), and moving on through powder adjustments only to return to seating adjustments, we've pre-conditioned the seating test results.
And this, I suspect, sways the favor to 'good enough' over 'best'..

For instance, I might pre-pick 5thou, or 25thou off, and hit on a charge with it that groups really well. If I then go back to adjusting seating, I will likely find that minor adjustments either way produce worse results. But this is because I'm now affecting the fortunate found results of my charge through tension, case volume, and distance to land changes(really chasing my tail).
What most people will see here is that it's far easier to stick with what they happened upon, and keep the seating they worked through charges with.
They would never know best seating, because they already moved past the test for it..

How many people assume jammed is a good starting point for load development?
And how could these people ever really go backwards to adjusting seating depth(often referred to as fine tuning), without mangling their tune too much to determine better seating options?
So I highly doubt they ever settle on another seating depth, without starting completely over.

What I'm suggesting is to pick a moderate charge, and determine best results with it -through seating changes. Do this right up front, and THEN move on through charges. With this, once you've hit on the best charge, you also know you're at the best seating, and so there is no reason to fiddle with either again.
Maybe the tune could be fine tuned -from here- with minor seating adjustment. But I think this is more likely to show your acceptable seating tolerance, than to provide actual gain.

I would think the both methods could potentially lead to a local minimum and miss the global minimum group size possible Isn't starting with a arbitrary powder charge and varying seating depth subject to the same critique as starting with an arbitrary seating depth and varying the powder charge?

Mikecr's comments about the primacy of seating depth really have me intrigued so I am going to attempt to test the independence of powder weight and seating depth on group size by tuning up the same bullet/powder combination using each method. I am concerned that the primacy of these variables may be gun specific, but I'll address that at some future date.

Method 1) Before finding this thread I was about 75% done working up a load based on a initial .002" off the lands COAL. I have the optimal powder weight narrowed down to within 1gr. For the next step I have prepared 50 loads in .1gr powder weight increments (5 rounds at each powder weight) to zero in on the optimum powder load for this seating depth. I plan to continue with this process to see what node(s) I can find.

Method 2) Based on Mikecr's comments I am going to try to identify optimal seating depth first and then optimal powder weight. To this end I have prepared an additional 20 loads with an arbitrary mid range power load that is about 6% lighter than I found to be optimal for the .002 off the lands COAL load. These loads start just touching the lands and then back off .01", .02", .03" and .04" (5 rounds for each COAL). Is this enough variety, or should I back off even more? I'll go to .001 increments to fine tune the COAL once I have identified the best seating depth at the .01 increment. Once the optimum COAL is identified, I'll start over with the powder weight optimization

Note that the bullets are Sierra Game Kings, loads are concentric within .001" and have meplats that have been uniformed. Cases, primers, trim length are all as close to the same as I can produce for all 70 rounds.

Any suggestions on how to improve this test would be appreciated. This is going to take a couple trips to the range and may take me some time to complete. I'll report here what I find.

Ha Ha! great thread, and well done Mikecr... i can relate to this entirely...

Initially, i did it the 'normal' way, and the way i was first taught to do it years ago... pick a seating depth, usually 20thou of the lands, or 'what everyone seemed to be doing with that particular projectile' and work up a powder/primer combination, then come back to fine tune the seating depth later.... Now, i do it the way Mickcr says...

The reason is, i noticed MUCH bigger differences in group size caused by seating depth compared with powder loads, same as mike describes. Usually, and using a mild load, i can barely see any differences in grouping size. So now, i simply pick a powder load that seems to be popular and is a rather cool load and work with seating depth first. All the cool loads ive tested so far, all seem to group quite nicely from a well built, highly accurate custom rifle. Its at the hotter end that things seem to get increasingly inconsistant, so any coolish load is a better starting point than an arbitrary seating depth IMHO.

I went to the range today with the loads described previously. As it turns out, for the seating depth test the best five shot group was with the bullets touching the lands. Even the .01" back didn't group as well. Since the "powder weight first" test was based on .002" off the lands, I am not sure my originally planned test will tell much. I did not fire any of the 50 loads with the different powder weights as I want to think about this awhile. Should I reseat these loads to the lands, or keep them where they are? My end in mind is an optimal hunting load and I may benefit from even .002" of tolerance.

The good news is that I did shoot a best ever group for this gun with Berger 168 VLD hunting bullets seating to the lands. I need to spend some more time with this bullet.