Earlier quoted context omitted.
Out of interest, why do you prefer a salt grinder? I've never understood why these exist. Pepper grinders, absolutely - the aromatics are released on grinding. By not so with salt. Curious if I'm missing something.
For pop corn you need fine grained salt. A grinder lets you control that. It is only about the grain sizes. Nothing about freshness with salt. With pepper it is about freshly releases aromatics.
I was recently planning to get back to a regular pestle/mortar setup after yet another costly failure. Did you manage to find a way to work this around?