I had something similar happen on a bear hunt. I have a cow elk muzzleloader hunt coming up soon during the "wet" season, and I picked up a kit at the sporting good store. It has the finger cots to put over the muzzle and a plastic ring that holds and seals a cap to the nipple. My hunting buddy recommended to fire at least two caps before you load to burn off any moisture/oil in the barrel, load, then pull the nipple and add a wee bit of powder there. This is for traditional open breach caplock rifles, not sure if you can do it on an inline.