I am assuming you have a cleaning jag with a patch wrapped around it stuck somewhere down the bore.
I had that happen and I made sure the jag was pushed all the way down the bore. Then remove the nipple, fill the bolster with powder, tapping the side of the rifle repeatedly until you don't think anymore powder is going in. It only takes 5 to 10 grains. Then replace the nipple and shoot the jag out. If you feel it might blow up, do what I did. I strapped the rifle to the railing of the back porch so it was pointing at the ground and rigged a string to the trigger. Then I let out enough string so I could go inside and pull the string to fire the rifle. It worked perfectly and the rifle is fine.