Unless you have a long history with a particular caliber, the process of reloading should be first to prove you have the proper headspace with your sized brass. Also, neck diameter WITHOUT a bullet will be smaller than loaded with a bullet.
Then, dummy rounds to find OAL lengths that load.
Until you know you have the proper headspace, A loaded neck diameter that fits into your chamber, then an OAL that is not jamming hard don't load live ammo.
Dummy rounds with minimum neck tension will sort of self adjust
Then, it's off to the range with LIVE ammo.