Hangfires are caused by many reasons. The hot shot nipple might be all that is needed. If not then the suggestions Triple Se7en offered will help.

A friend's son bought a new rifle and brought it over to the house to shoot it and learn about muzzleloaders I guess. That was the most hang fire/miss fire monster I ever saw. I gave him a new hot shot nipple out of my supply and that did not help. So I took his rifle to the shop and blew the bolster out with an air compressor, and that did not help. I alcoholed the barrel and still not good. I then tried some hotter caps and still hangfire or misfires from him. I beat on the sides of it and did everything I could think of. I was at wits end. Then I saw the Pyrodex he was loading and asked how old it was. Turned out it was about eight years old. So I told him to hold on a second...

We loaded his rifle with my Goex 3f and if purred like a kitten....

All you can do is play with them. I have one side lock that I can not swab the bore with anything other then pure alcohol. Anything else and it will hang fire or miss fire....

Keep us posted and glad it is still a shooter....