Red_Eagle,
You're starting out with a false premise. The idea that you have to get a bullet close to the lands for good accuracy is untrue. Some rounds actually work much better with the bottom edge of the bullet bearing surface seated about one caliber into the case mouth. This seems to be more true of light bullets than of heavies, but every gun is a law unto itself, and you just have to experiment to try? To find a seating depth sweet spot, you will have to experiment, but I would start with 1 caliber into the case mouth and, using a mild starting load, seat both deeper and shallower in 0.010" increments until you find minimum group size. Once you have that, start tuning the powder charge to shrink the group further. When you know what your sweet spot depth is for a particular bullet, measure that with the Stoney Point tool and keep a record so you can replicate it with future setups.
The main advantage to seating just off the lands, a common practice with match chambers with their short throats, is that the bullets can better self-align in the throat of the bore so the tip is cenetered in the bore. Slight bullet tipping on entry to the throat can cause up to a moa or so of group size increase. There are, however, other strategies for getting good bullet alignment, base on getting the bullet lined up properly in the cartridge case in the first place. A good start is to use a sleeved match seating die such as the Redding Competition Seater Die. Other brands, like Forster, make these sleeved seating dies, but my only experience is with the Redding, which is wonderfully accurate. My plain seaters allow up to 0.008" total indicated runout (TIR), while the Redding allows maybe 0.0005" TIR if my cases are perfect. If the case has uneven neck wall thickness, that reads as added TIR on a gage, so don't be fooled by that. You will want to buy or build a cartridge runout gage to check your ammo.
Another helpful strategy is to neck size-only so the fireformed cartridge case centers itself in the chamber. If you leave the last little bit of the neck unsized just ahead of the shoulder, that will center the bullet in the neck portion of the chamber. The Lee Collet Dies, though a little tricky to learn to work with, will do that for you, and they are inexpensive. The only issue I've seen arise with this is when a chamber is slightly off-axis from the bore. You can address that by always loading your cartridges with the headstamp in the same orientation in the chamber. Neck-sized rounds need to be loaded singly anyway.
The figure of an moa group increase from bullet tilt that I gave comes from a study in the out of print NRA book, Handloading. It was done with M72 match ammo, IIRC. This was .30-06 that was new Lake City ammunition, not reloads, and not, obviously, fireformed to fit the rifle chamber. Nonetheless, by measuring cartridge runout and shooting 800 some rounds in the test, they found that 0.004" runout could make that much difference on the target. More runout than that did not make it any worse as the bullet could straighten itself out from tilts above that number. This was a 173 grain boattail match bullet, very similar in shape to the 175 grain Sierra MatchKing, though less well made. Seating depth was within SAAMI maximum 3.340" for .30-06, yet the match rifles shot them very well.
Below, I'll post my bullet nomenclature diagram just so anything I mentioned above about where the seating goes is clear.
