AH! Are you using a thin pick to open a hole in the powder charge as it sits in the flash channel on that rifle? If seating a PRB or any kind of wad forces both air and powder down into that flash channel, it can pack it tight. That is why I recommend using FFg powder in flintlocks. It doesn't pack so tightly. However, in patent breech guns, you are almost forced to use FFFg powder in order to get some granules close to the Touch Hole.
If there is NO powder in the flash channel, you are almost guaranteed to have a " flash in the pan", because the heat of the flash cannot travel all the way down the flash channel to the center of that powder chamber in the breech! YOu don't want the flash channel packed solid, nor the Touch hole closed because powder is packed full and tight at the entrance. Instead, the goal is to have SOME powder in the flash channel, and an open vent so that flame and heat can start more than one or two granules right at the mouth of the TH.
Close the frizzen before loading the powder and PRB down your barrel. Then, use a thin wire to open up a hole in the powder located inside the TH in the flash channel. Now prime, and close the frizzen again. You should be fine.
With those flash channels, I would rather see you open up the flash channel one drill size, and polish the heck out of it, rather than being drilling the TH larger. The larger flash channel will elongate the hole into the powder chamber, making it easier for powder to come through the powder chamber, into the flash channel when loading. By closing the frizzen, you prevent a lot of powder from being blown out the vent and lost, affecting your consistency of velocity, and therefore accuracy. Take care in opening your frizzen after loading this way. you may find it full of powder already, especially if the TH is too large! :shocked2: :thumbsup: