Drop the ramrod in and mark off on the ramrod where it stops. Then remove the rod. Afterwards, pour a small amount of powder into the barrel via the touchhole and making sure the muzzle is pointed in a safe direction, fire it off. Then reintroduce the ramrod to see if it is clear or to measure how much further down the barrel that critter went. Repeat the process until it's clear.
Alternatively, you can have the breechplug pulled and use a dowel rod & mallet to drive it out. Be sure the breechplug is marked so you can get it realigned when you reinstall it. Remove the barrel first and clamp it in a vise. Be sure to have copper plates or leather pads so as not to mar the barrel. Then, to remove the breechplug, you can use a crescent wrench and wrap some leather around the tang. Get as close to the thick part of the plug as possible. Give it a few turns counter-clockwise until the plug is free from the barrel. Drive out obstruction, clean out the bore and the bottom of the breechplug, and then reinstall.