I just picked up the correct tap a long time ago and make my own cases to fit the Stoney Point threads when the need arises.
When you put the loose bullet in and run it up to the lands how do you do it, and how can you do it consistently each time? How do you know that you have precisely and consistently put the bullet right at the lands each time by dropping a loose bullet into the chamber and then pushing it up into the lands? How do you hold it in place precisely and consistently each time at, but not into the lands, to get the clamps set? I never have trusted this method to give consistent results. Remember you are seating a tapered object into a tapered hole, but one that isn't smooth but has sharp lands etc., so precision and repeatability are important. You're not setting a flat surface against a flat surface.
Your current method will give you the COAL with that particular bullet, but only with that particular bullet. Switch bullets and because of tip variations you will not have the same measurements. The measurement to the ogive is much more consistent and repeatable.
I assume you take the COAL you obtain by your method and then set your seating die to give you a loaded round that is the same measurement from the base of the case head to the tip of the bullet. When you set your die for that case and that single bullet you now have that particular round loaded to a given length that hopefully would give you a loaded round with the bullet just at the lands. Load another bullet and measure and you will probably end up with a different COAL because of tip configuration variations.
Even though you got fairly consistent measurements from the three tries with the same bullet that just means that if you seated that bullet in a case that you would have a COAL that would give you a round with "that" bullet loaded to the lands. Take another case and another bullet, seat it with the same die setting and what do you think the result would be? What you want to obtain is the most precise, consistent loaded dimension from the base of the case head to the ogive of the bullet. It is the ogive that is going to contact the lands, not the tip of the bullet. Measure a bunch of bullets for oal with a good micrometer, base of bullet to tip of bullet, and see what you get. Then do the same thing with the proper gages from base to ogive, or the way I do it, by using dual gages set to the ogive contact diameter of the caliber you are using. Then see what your measurements are. All bullets don't tip up the same during the forming process but the ogive dimensions are pretty consistent. I think that you would be better served using the ogive as a measuring point as compared to using the tip which is very inconsistent. This is all just my opinion and methods and all of this nitpicking is meaningless at shorter ranges, but........this is a long range forum and at extended ranges everything is far more critical and important.
Now for something else to play with, set your seating die, using whatever method you use, to a setting that will give you a COAL at the lands. Load up 20 or 30 rounds at this setting. Now, using the right gages, measure from case head to ogive on each loaded round and see what you come up with. Do this and you will see why some reloaders load all rounds long, measure base to ogive, segregate, and then adjust for different length groups and reseat so that all are at the same base to ogive measurement. Not necessary unless you're a little anal, but it can be a fun exercise. If you believe that by increasing or decreasing COAL and thus the distance either into, or away from the lands means a different pressure and thus a different pressure will probably create velocity differences and different velocities will create huge vertical differences at 1000 yards or more and see what you think is important.
