Don't use modern chemicals or boiling water
Hot water and Dawn is what I use. Do not use modern chemicals, most will react to blackpowder and cause corrosion. Most today cleansers are meant to cut through rough dirt and that alone will work against your barrel. After rinsing with warm to hot water, dry the best you can, breaking it down as far as you can. Turn it upside down for the night. Now spray the parts you can't get to with WD40 to get to water that might still be there. Oil the gun like you would any other gun and wipe it down. Remember that WD40 is a rust remover and water displacer and it will dry out. Like other guns you handle you should do them every several months.