I use about a half pan (FF or FFF usually). When I close the frizzen, I turn the gun so the lock is up, and give it a couple of mild thumps with the heel of my hand to shake the powder into the flash hole, after which I rotate it so the lock is down, and give it another thump to shake the powder back to the outside end of the pan, and it's ready to go. I believe that this method leaves a fine dust of powder into the flash hole (NOT a fuse trail), and the flsh is enhanced a bit thereby. If you leave a fuse trail, it will be slower because the flash has to burn thru the powder plugging the flash channel, rather than flashing through at the speed of the explosion expansion. If in a hurry, I leave out the thumps part, and just place the prime at the outer end of the pan. Try it all; find out what works for you.
That's what I've been doing with my Kibler .45 SMR, but I suspect it's overkill. Next time I'm out alone instead of babysitting friends and coworkers, I'm going to start bringing the amount down and see how much I really need. And yes, I also use 3F for both the prime and the charge.I fill up the pan till the powder meets the bottom of the flash hole while the pan is level. 3F is what i use.
When I first primed a pan I filled that sucker plumb to the top and a big swish and no boom. Took a while to learn, but I accidently discovered a grain of powder will set the charge off.