Do you swab between shots ? I am of a habit of swabbing between shots with a patch sprayed with some 71% alcohol and then followed with a clean patch. I run the wet patch down and then flip over and run down again,then do the same with a dry patch, then load. I am not having any problems with my two Lyman GPR or my New Englander. Seems the patent breech the norm of the mass production world. I am to old to change now but I look back and wish I would have just had one nice Flint Lock customed built and been done with it. We all have hindsight, just never seems to be enough money though.
The patent breech does add an extra process to my cleaning ritual. I first use a breech scraper, followed by a 36 cal. bore brush , then I plug the touch hole or nipple and fill the bore with a mix of Ballistol and water or Dawn dish soap and water and let it sit for at least 10 minutes, after which I just do the normal stuff with the pumping action with range rod and patch.When I dry, I wrap a cleaning patch around the 36 cal. brush and give that some twists down in the breech, same with adding some rust preventative oil of which I only use Barricade for that, nothing else. I lube my patches with TOTW Mink oil. So far,no miss fires or flash in the pan poof.
Good luck!