Just for the heck of it try a different method of measuring COAL.
Run a fired case into the sizing die just enough to resize about 1/8" of the case neck. Seat a bullet long by hand, chamber the dummy round, close the bolt, remove and measure. Repeat to verify.
Nothing like simplicity. I also soot the bullet so I can see if the lands grab the bullet and pull it out a bit upon extraction. This does happen, but if you soot the bullet, you can see exactly how far the bullet was pushed in by the lands, even if it does get pulled out a bit. Works every time and is a pretty damn accurate and easy way to find max OAL (aka lands)...
