I proceeded to measure 100 bullets from the base-to-ogive (BTO) and they ended up in 11 groups ranging from 0.588 to 0.574 inches. The difference suggested to me that if I seated the 0.588 bullet 0.02” from the rifling (leade), the longer 0.574 bullet would end up 0.014” further away, or 0.034” from the rifling if I seated it at the same die setting.
I did not read every post in this thread so apologies where applicable if I am repeating something that has already been pointed out
bullet base to ogive will only affect the case volume of a completed round, not the base to ogive. The base to ogive is indexed off of only two points of contact. The cartridge head sitting on the case holder and the stem of the seating die.
Depending on the cone shape and depth in the seating die stem it is possible that the stem is contacting the meplat not the ogive of the bullet thus resulting in different cartridge depth to ogive measurements. A quick way to check this is measure the overall depth of several cartridges and if the base to meplat is the same on all yet the base to ogive is different you have isolated the issue