My 500cc .25 only needs to be on setting 2-4 for JSB 25.43 & no more than 6 for 33.95. If you shoot anything other than Eun Jin or slugs on anything from 8-13 the soft lead pellets will be ripped apart.
I usually shoot 20 grain FTT on 2, 25.43 on 3-4 & same for 33.95 unless I’m reaching out far, than I might go as high as 6 but faster means more drag so you’ll need some JSB 25.43 33.95 & Eun Jin .22’s.
Anything else, even 21 grain Kodiaks, start on a 3K fill & power wheel bottomed out (1) try up to (4) for a 32-50 yard zero & learn your dots on whatever magnification you like.
Slug your barrel if you have micrometers. Mine is a 253” .25