Working on my new artillery piece. Doing some chamber data. For my rifle I start getting a sticky bolt at 2.325" shoulder length. I have some multiple fired Lapua brass that is now reading 2.327 or less. As my cases fire form, I start bumping them back when case length gets to 2.325" or better. I bump back to 2.324" - 2.323" so a .001" - .002" shoulder bump. Seems to vary based upon load how fast they stretch which would be as expected.

I started looking at seating depth using a Hornady OAL guage. The modified case is 2.317" but all my brass is 2.323" or so. I determined that to get an accurate seating depth the only apples to apples measurement was the shoulder to ogive measurement. This is what I have determined so far:

300 SMK
Gauge measurement 2.829"
Modified case length 2.317"
Shoulder to Lands .512"

So to seat my bullet length touching the lands I have to add the shoulder to lands measurement to the case length being loaded. So if I am loading a case which measures 2.323 to have a 300 SMK bullet touching the lands I have to have a base to ogive length of 2.323" + .512" or 2.835"

What seems amazing to me is the 300 bergers, the 300 scenars, and the 250 SMK all have a shoulder to ogive measurement of 0.522"
The 285 hornadys have a .538" shoulder to ogive length