Then I would question a few things... What are his loading procedures? Is your friend making sure the barrel is oil free and dry before loading? In a case like what he is experiencing, I would hunt on a fowled barrel. Have his drop 20-30 grains in the barrel and a wad on that. Then fire it off. Now reload. This way he knows the gun is dry, the nipple is sparking well and the gun will go off. Also make sure he pops three caps through the nipple before loading to make sure the fire is getting into the breech. This can be checked by putting a cleaning patch on the jag and push that into the breech and pop some caps. Then examine the patch and make sure it has burn marks on it which indicate that the fire is getting into the breech channel.

The other thing I would do in his case is change over to a stainless steel Hot Shot nipple if he has not done so. They seem to produce much more spark into the breech. In fact if musket caps are legal in your state it would not hurt to have him change over to a musket nipple if one is made that will fit his rifle. Thunder Ridge carries the musket nipple that fit most sidelocks.

Also make sure he is picking the nipple before capping the rifle. If he is not taking measures to weather proof the rifle then he should do that also. Another thing I do is when hunting I change the caps over ever three hours.

Be sure and follow climate control of the rifle at all times. Don't bring the loaded rifle in from the cold into a warm house or car where it can condense moisture in the barrel and contaminate the charge.....