A few questions:
First, how do you clean the rifle after each session? Do you flush the breech with water to ensure that the flash channel is clear?
Second, in what position do you store the rifle? In my experience it's best to store rifles with patent breeches like your T/C muzzle-down, so any excess oil in the bore drains away from the breech.
Finally, are you swabbing between shots? If so you may be pushing fouling down into the breech, causing the misfires. When I shoot at the range I use a wet lube that allows me to shoot as long as I want without swabbing. In effect, you're swabbing each time you load but the fouling doesn't go past the powder charge into the breech. In my experience this makes my rifles more reliable.