I have some specific OAL questions, but still digesting lots of info and doing my due diligence to figure this out before I ask for confirmation that I understand it. However, after sitting here for a couple of days with dimension diagrams of 9mm rounds, calipers, and a smorgasbord of different weights and profile bullets, it seems I was wrong thinking seating is standardized. I assumed that no mater the bullet profile, so long as the weight is the same (e.g., 124gr), every bullet, regardless of profile, would have the same amount of material seated in the case and the 'usable cavity' would be the same to standardize pressure across profiles...if that makes sense. I assumed that the differences would be in the shape OUTSIDE the case. This isn't true, is it? In my tests, were I to load to an OAL of 1.142 as called for in the recipe I am analyzing, roughly ~.150 of a 124gr TCFP would be seated in the case, whereas ~.190 of a similar weighted RN would be seated...holding the OAL constant. There isn't some unwritten rule about >25% or whatever % of the bullet must be seated in the case for stability/pressure/whatever reasons? I am still working on my question but it has to do with 2 different loads published for two different 124gr bullets, yet there are a dozen or more combinations of plated and coated and truncated and flat point and round point, etc, etc, etc...and both recipes call for the SAME OAL....which got me thinking—no way, can't be. Seating some considerably deeper than others changes pressures, so if creeping up toward maximum load, I could get into trouble trying to seat all these different profiles the same OAL (and toss in the fact my Glock likes shorties and I am getting nervous)...but that's another thread as I research more and gain a better understanding.