ORIGINAL: Semisane
In my range sessions with the .54 GP, I've been gradually reducing the amount of powder I put in the pan to see what happens. What I've found is that it takes very little powder to get reliable ignition. In fact, I get the fastest ignition with the smaller amount. The picture shows how much FFg I was using in the pan for the last ten loads in my last range session. Every shot went off, and (I believe) just about as fast as a caplock.
Most experts with FL recommend 1/3 pan. If you fill the entire pan, thinking it will "go off better/faster", the spark has to burn down thru the powder then thru the touchhole to ignite the powder in the barrel, so basically your trying keep the powder below the touchhole. Here is some good tips on ignition:
http://www.blackpowderjournal.com/archives/vol1no4/articles/ignition.htm
Chap Gleason