A LOT of water has passed under the bridge since I first posted. I'm still very much in the persuit of accuracy.
First, by WEIGHING every bullet I've learned a lot about refining every aspect of casting bullets. Reducing 200-250 gr bullets to a variation of +/- 0.1 grain was a goal and with some moulds achieved. Took some time. But WEIGHING provided the feedback directly about variations in all the things that go into making the bullet.
Second, running (5 shot) groups across the range and wider, of recommended published charges got me NO WHERE in trying to find a good load for a known accurate rifle. Then in frustration, I picked the load with the least vertical dispersion and varied the seating depth. Groups went from crap to excellent to crap. BINGO!
3 shot groups are OK. I shoot 5 shot groups to get a little more info. I make the distinction that one should use the group to REJECT unworthy loads. Across the board when one shoots 5 to 7 groups (of whatever count) spaced closely together it is obvious when one compares the sequence of the patterns. REPITITION alone will verify that one particular group was representative of the population. And when it gets close, I'll repeat and do 5 five-shot groups.
It's typical from my observations to note that the shape of the group will typically go from scattered to horizontal to diagonal to vertiacal to scattared. Somewhere the vibrations are good and the size with be right-much small.