Remove the barrel from the stock first. Then get a Tea Kettle and boil a kettle of water. Take the barrel outside and remove the nipple from the bolster. Squirt a good shot of dish soap down the bore of the barrel. Have a long ramrod with a .50 caliber brush on it. And some leather gloves. When the Tea Kettle is boiling, then pour the barrel full of HOT water. Grab the barrel and work the brush up and down through the bore. And after a couple good scrubs... fill the barrel with hot water. It will float and wash a lot of the packing grease out of the barrel.

Now with the barrel hot. Take it inside, and with a cleaning jag start working solvent patches down the bore. This will pull additional grease and crud. It will also help make sure that the barrel is dry. Once the patches come out clean, then dry patch that barrel until the patches come out dry. Now with a good gun oil, apply that to a patch and swab the bore of the rifle with that patch. This will coat the barrel and as the barrel cools, it will draw that oil into the pours of the rifle.

Now put a white paper towel or white cloth on the ground in the corner. Set the barrel in the corner muzzle end down and let it cool for a couple hours. As it sits there muzzle end down, any excess oil will flow away from the bolster and out the barrel onto the paper towel.