Typically, hangfires are caused by:
Using a Black Powder substitute like Pyrodex, 777, etc.
Leaving a spent cap on the nipple or leaving the hammer down on the nipple when ramming the patch/ball down the barrel.
Oil or other liquids left in the flame channel (a small hole) which runs from the nipple to the bore
Fouling left in the flame channel from incomplete cleaning
A plugged nipple
Debris knocked loose from wiping the bore between shots.
Fixes to the above problems are:
Use real Black Powder if you can get it. It's ignition point is below 500 degrees F as compared with the 800+ degrees the replica powders require.
When loading, make sure the hammer is at half cock and there is no cap on the nipple.
Remove the nipple and run a pipe cleaner down thru the flame channel hole. Also, do not use excess oil to protect the bore. It often runs down into the flame channel where it will contaminate the loose powder granules in that area which promote ignition.
When cleaning a percussion gun, run a pipe cleaner down thru the flame channel to remove fouling.
Use a nipple prick (or a very small wire) to assure the passage is open.
When wiping the bore between shots use a lightly moistened patch on the jag. Push it to the bottom of the bore, count to 2 and then pull it back out.
The downstroke will wet the fouling, the count will allow it to soften and the upstroke will remove it.
Do not pump up and down on the rod or run a dry patch down the bore as this will knock the fouling loose and allow it to collect in the bottom of the bore where the flame channel is. Pumping up and down will blow the loose fouling debris into the flame channel where it will block the loose powder grains and the flame from the cap.
There are more things that help like exchanging the factory nipple for a Hot Shot or Spitfire nipple and using CCI Magnum caps but the bottom line is this: These are old fashioned guns using old technology and even the best of them will sometimes hangfire or misfire. It goes with the beast and when everything works like it is supposed to it makes a traditional muzzloader shooter grin from ear to ear.
zonie