Mine's still on the original nipples (Although I do have a spare set from Tac) and I have endless problems with CCI primers. Unfortunately anything else seems hard to find. When I used Remington, it never missed a shot. You're right that it is to do with them not seating properly but even if I push them on, I usually get one or two misfires out of 6. Maybe I should try chamfering the nipples but, as I say, other primers are fine.

I use round ball - .457
I use 777 exclusively and for me, target shooting at 20 - 25 yds, I find 15 - 18 grains fine. I've tried heavier loads and while the bang and flash may be impressive, I've not seen an increase in accuracy! I've tried inert filler and commercial wads but now use wads punched out of a Pilates mat! i.e. A fairly dense foam rubber. Not much to choose between any of them as far as I can see.

Do bear in mind that every single ROA shooter in the world will have completely different views on what is "best"

Steve