boats wrote on May 28
th, 2020 at 9:09am:
Rambling no hard opinion & addressing seating depth not loaded cartridge consistency. Core issue I can see any method to check consistency needs a uniform “datum” that is a single consistent reference point on the object being tested.
Reference point on the commercial comparator tools I have seen is cylindrical, reliable standard. If the nose is not consistent the reading won't be consistent which may be a good thing to know.
Pure opinion, all of the methods guys in this forum have mentioned are probably better to set bullet seating depth than any tool. Bullet you will use in the chosen guns chamber without any extra tools.
I slip fit the bullet in the case or breech seater, paint the nose with black marker chamber and look for indication of engagement. It's just a starting point, pass that simple test how the load performs is the real test.
Boats
The idea of a comparator is not really to set seating depth, only to check it.
You start with any of the methods talked about to find the lands, then measure that cartridge.
Then set up your seating die based on that measurement using the tool, and whether you want say .015” jump or jam. Once you’ve found your accuracy length, it become easier to repeat setting up the press.
When you want to start spilling hairs, then sort your bullets first, base to ogive. Then the loaded length will be a tighter tolerance. Seated depth/compression, as well as jump or engraved depth into the bore.
The other thing that can be done is to save the original bullet and case used to take the measurement. You can use it to measure throat erosion later on.