rafsob;i've never shot the FPB's but i do shoot blackhorn out of my vision and have never had a hang/misfire with it.i use a tight dry patch both sides and then a pipe cleaner and wire to clear the breechplug.i also use 100g Bh209, 250g barnes tipped boatail with supplied yellow sabots ignited with W209 primer.did you use a 1/8" drill bit to clean the carbon out of the breech plug?the one time i cleaned out a breechplug with a primer before i patched the oil out i had a hell of a mess to clean out.i think if you had oil in the breech plug when you popped those primers you might have a heavy build up of carbon/oil stuck in there from the begining?i've done about 20 shots during my range outings and afterwards did have alot of carbon build up.how easy do those fpb's load once their started?do you think they sit tight on the powder?good luck......karl