If you shoot muzzle loaders, sooner or later you experience a blocked barrel: either a powder charge that won't go off or a ball seated without powder; or perhaps you will acquire a muzzle loader with a blocked barrel or even a charge still in the barrel. In any case, it will eventually happen.
Sometimes a ball screw will extract the stuck projectile; other times a silent ball discharger will do the trick. Both of these are relatively expedient fixes to the problem. However, there are those times you will encounter when neither of these fixes will work. What then? Well, there are many different approaches, but the one outlined below is my favorite. It works 100% of the time, won't damage your gun, and poses no hazard, even with a live charge in the barrel.
Simply remove the nipple from your gun and screw in an automotive grease zerk in its place. These automotive grease zerks are the ordinary type found on tie-rod ends, ball joints and other automotive chassis applications. They are manufactured in both SAE and metric thread pitches. So far I've managed to find grease zerks to fit every muzzle loader that I've encountered.
Once the zerk is firmly screwed into place, attach either a hand pump, lever type automotive grease gun or a pneumatic grease gun to the zerk and begin pumping. The hydraulic pressure of the grease in the barrel will positively dislodge a stuck projectile and/or powder charge, including shotgun loads! Once the blockage has cleared the muzzle, remove the grease zerk, and give a shot of compressed air into the nipple hole, while the muzzle is pointed into a bucket or gallon can. Most of the grease will be blown clear of the muzzle, thus minimizing the cleanup process.
To really minimize the cleanup necessary with this little procedure, buy an inexpensive, bulk type automotive grease gun, and rather than filling it with automotive grease, simply fill it with vegetable shortening! The shortening will work the same as automotive grease through the grease gun. Cleanup is much easier and quicker than when using automotive grease as well: after blowing out the majority of the shortening with compressed air, simply heat the barrel until the shortening melts and pour the remainder from the bore, swab it out with a patch or two, and you're done!