Had a Pedersoli Mortimer about 20 years ago. Ignition wa awful. Then I read a piece by Ross Seyfried on his experience with the same rifle. Followed his directions and opened the hole to .0625 and coned the backside so the main charge was very close to the hole. Ignition after that was fast and sure, seemingly as fast as percussion. Actually, I did the modification on a spare one, and kept the original as-is, just in case. I suggest you have a spare, and test both for good ignition, but suspect you'll never wear one out. I rotate the breechplugs of my inlines the same way.
I've read that old military guns like the Brown Bess used to erode pretty badly, but thise barrels were probably pretty soft, and those guns stayed in service for a long time. In one of the Bernard Cornwell novels about Richard Sharpe, he teaches soldiers to give the musket a sideways kick instead of priming from the cartridge when pressed for time. The holes were large enough that powder would flow into the pan from the chamber.
Had to let that one go, regrettably, and new ones are outta sight, but they are fine rifles.
