As you've noted, the Pedersolis usually have a "patent breech" with a VERY small "chamber". There are valid principles of internal ballistics behind this design for more efficient burning of the charge, but it makes getting powder reliably down to the touchhole problematic - the powder can bridge at the step-down. There are two standard cures applied. One is to pour the powder slowly and/or tap the the side of the butt or opposite the lock after you pour the powder but before ramming the ball (doesn't help once you've rammed the ball and packed the powder), to settle powder into the patent breech. The other is to drill the "chamber" out somewhat larger. I had the one on my .50 opened to ~.30" as a compromise, but it still bridges over occasionally even with 3Fg, so I usually still slap the side when I load. For comparison, I have a 16ga with similar breeches but with the chambers something like .35" or a bit larger, and I have NEVER had to fuss with it - dump powder, insert wads, and ram.
The dictum about keeping your priming toward the outside of the pan seems to have come from avoiding covering the touchhole and/or forming a fuse by filling the touchhole with priming powder. These WILL cause a notable delay in ignition. A properly designed internally coned touchhole (usually a liner nowadays) largely gets around the fuse because the small-diameter portion of the touchhole is very short. I don't know the vintage of your firelock, but the newer Pedersoli touchhole liners seem to be well coned internally - but often with a slightly small touchhole. As mentioned, drilling it out to 1/16" often improves reliability, and if that doesn't cure flashes when the powder is in the breech, then enlarging the touchhole and testing is the usual route, going up by one or two numbered bit sizes at a time up to maybe 5/64" max. Of course, none of this helps if you have crud blocking the touchhole.
I hope this is of some use,
Joel
The dictum about keeping your priming toward the outside of the pan seems to have come from avoiding covering the touchhole and/or forming a fuse by filling the touchhole with priming powder. These WILL cause a notable delay in ignition. A properly designed internally coned touchhole (usually a liner nowadays) largely gets around the fuse because the small-diameter portion of the touchhole is very short. I don't know the vintage of your firelock, but the newer Pedersoli touchhole liners seem to be well coned internally - but often with a slightly small touchhole. As mentioned, drilling it out to 1/16" often improves reliability, and if that doesn't cure flashes when the powder is in the breech, then enlarging the touchhole and testing is the usual route, going up by one or two numbered bit sizes at a time up to maybe 5/64" max. Of course, none of this helps if you have crud blocking the touchhole.
I hope this is of some use,
Joel
