Generally trial and error until I get the feel I want. Set up a build one way, try it out. If I find myself running out of of ammo, not doing enough damage, etc, I’ll try to remember that and adjust for next time. Although by this point I’ve played so much all of my guns are pretty locked in and I think I would get confused if I changed OCs now.
I did greatly enjoy the new set of OCs they released. Using most of those now.
Is this science tho? More like statistics if anything. I don’t see any hypotheses being tested.