WRT the primers... lacking a chronograph, and using SPM primers, and knowing that the load functions in your gun, and is accurate, you could just leave well enough alone.
Even though I have a chronograph, for range ammo, I often use the start data, and if it functions and is accurate, I usually call it good. I don't have any good reason to experieince more recoil or muzzle blast or beat up my gun, or my hand.
On the other hand if I wanted to duplicate the recoil and POI of a defensive carry load, I have my chronograph, and I can do that too. Working up safely while monitoring function, velocity and POI on the target.
I would also use the chronograph when working up a load for hunting or match loads, since they will generally not be the start load, and usually somewhere near the max load. The chrony will help tell me when it's time to stop, regardless of what the data book says.
The exception to that would be the .454 Casull I use for whitetail hunting... the .454 is overkill for whitetail, and the starting loads are more than enough punch, as long as I get reasonable accuracy.