Indeed, I can't imagine you getting a miss-fire with a coarser granulation of powder. Possibly slower...but the old adage holds true that every gun is an individual, so some may fire faster with ffffg, some not. I use ffffg because I have plenty of it, I wouldn't hesitate to use fff, ff or even fg if I wanted to, needed to, whatever. My Jeager has incredible lock time with ffffg, so I'm not sure why I would change that, or try anything different.
On 4fg being more prone to moisture, I found, a long time ago, that most (not accusing anyone) guys who had trouble with moisture in their pans, were the same guys who washed their locks in the dishwasher, or with soapy water, dried them off and then hosed them off with WD40, or something like that, wiped them off and SHAZAM they was done cleaning. What was really happening was that the oil was migrating up from the lock, in between the lock and barrel, and into the pan. So, if one has trouble with the prime "absorbing moisture from the air", one might want to try removing all oil from the lock, and greasing the moving parts instead. Or, de-oiling the lock, and then re-oiling very very very sparingly. ??? Just a suggestion.