Most old-school machinists will tell you that a caliper is the wrong tool if you need to guarantee better than 0.002". A micrometer is the called for, for anything finer. I think high quality calipers are probably a little better than that, but pretty much ignore the ten-thousandths digit.
I'd suggest getting things as consistent as you can, then let the paper tell you what's working...
GsT
Well being an old school tool maker of 50 years, I have no problem reading to .0005"
with my Staretts or my bench NSK as long as it's a 100 thou dial. I do not recommend
digital which is all the rage these days. That's old school.......There is this mention of a
seven second hold time for brass spring back on a shoulder bump. The missing piece
to this equation is the annealed properties of the brass. I anneal my match brass after
every firing. No dwell time is ever needed. and that was with my Norma brass or now
my mostly used Peterson brass.
Gator......Your mention of hitting a 2.1 SD in your 30/06 is admirable. Trying to keep it
there has one basic issue with it's very long powder column. In that case, powder choice
can be a very hot topic. Some will tend to try a powder in slower ranges where the older
powders in the 4064 ranges can prove better. It's all about working with that long powder
column. Competition reloaders figured out long ago to use that same boiler capacity but
in a much shorter but fatter case. Think why the .284 Winchester became the go to for the
longer ranges. Very hard to find anyone competing in anything with the 06, but I for one
will want you to get it worked out......
