Fastest way I know of, if you are not set up with a boiling tank and apparatus, is to pour boiling water over the barrels while they stand vertically. One of those old big coffee pots on a hot plate will hold gracious plenty water to heat the barrels evenly to that temperature. Try standing the barrels in a bucket, muzzles down and pouring the boiling water over the breech end, allowing it to drain down the barrels into the bucket. They will dry instantly after you lift them out.

SRH

May God bless America and those who defend her.