Re: hand priming tool or automatic priming tool from RCBS?
It is crucial that the primer is contacting the pocket base. With this & no striker or headspace problems, the primer will ignite reliably.
But mere primer ignition can still leave degraded load performance, from higher ES to flat out flyers, and in ways too abstract to lay down as a rule really. This leads reloaders to 'trying' different primers & picking what seems best for a load(for some reason). Few dig in to figure out the whys, but some BR shooters have been left with no choice and have found issues with firing pin settings, or trigger drag, cocking piece misalignments, or spring issues, etc.
Of all the books I've read, I've never seen a study on primer ignition w/resp to speed, indentation depth/dia, or even overall energy. Having run into an issue with this once, I can say that both the magnitude/difficulty of the problem and the resolution shocked me. It could have happened to anyone and they might never have gained awareness of it.
There is a lot to learn here.
And we're not gonna learn it from PB BR shooters, as mere ignition even with fairly big variance won't affect N133 & +75Kpsi loads in tiny 6PPC cases -much at all. So they can get by with smashing primers flat enough.
Different story with more of slower powders and normal pressures. Truly, pretty much everything is different here.
So it will be LR shooters, probably hunters, who work it out.