Re: Seating depth vs Pressure
Personal experience has led me to the same conclusions as SBruce and the rest. Seating into or very close to the lands WILL increase pressures. I experienced the same thing you are asking about in my 338 Khan a few years back.
I was seating bullets hard into the lands and like you was running right on the ragged edge of having pressure problems, hard bolt lift, lose primer pockets, etc. When I started seating the bullets .015 off the lands the pressure signs went away and I was actually able to increase the powder charge and gain significant velocity with no pressure indicators. To me, this indicates that a bullet seated very close or into the lands can create an initial pressure spike.
It is true that if you seat bullets very deep you can decrease case capacity and cause an increase in pressure, but the difference of .002 off the lands to .025 off the lands is so small a difference in case capacity to make little if any difference in pressure due to case capacity. With my Khan I had it throated long so I could seat a 300 SMK way out there and gain some case capacity. This does work, but we are talking much greater seating differences than just a few thou.