I would have to agree with Semisane on this. None of my rifles would ever even leave the bench with a projectile in it. If it were a hang fire and pan didn't ignite I would wipe, adjust, or replace the flint. If the pan ignited but not the main charge I would clean out the flash hole. If a suspected dryball I would remove the lock and flashhole liner, put in some FFFFg, replace the parts and try to expel the charge into the ground where I could see the bullet hit. If none of that worked I would get out the bullet puller and get that projectile out.
The only time I ever put a charged sidelock in my vehicle is during hunting season. (In PA a ML is not considered loaded unless it is capped or charge in the pan.) Even then I put a tire valve cap on the nipple or, in the case of a flinter, a paper towel or patch between the flint and frizzen.