Hi, Carpediem!
The correct seating depth all depends on the caliber, type or nose (length of ogive), length of bearing surface, presence/absence of bore riding section, an a WHOLE BUNCH OF OTHER FACTORS!
My friends and I have loaded and shot cast bullets for close to 30 years, and nothing short of lots of controlled experimentation will give you that optimum combination for best accuracy.
Not trying to be evasisive, but it REALLY does depend on the exact bullet, cartridge neck length, throat depth and diameter, and condition of bore.
I've almost always had best results with bullets having a long bore-riding nose. A classic example is the Lyman 311291 gas checked RN designed for the .30-30. It casts at about 173 grains. I get 100 yard groups of 1" to 1 1/2" consistently in calibers .30-30 Win, 308 Win, .30-06. It will do nearly as well in .30-40 Krag and .300 Savage. Best seating depth (in different rifles) varies from touching the lands, to 0.020" to as much as 0.050" short of the throat. You have to play with it to find the best place.
HTH
John
