Plug the chamber using a collapsible ear plug. Give the muzzle a one second squirt of Wipeout and let the gun sit overnight.

The next day I'd empty the wipeout, brush the barrel (many use a stiff nylon brush) I use a phosphor bronze brush and finish with a dry mop.

There's a lot of products used for copper solvents and Kroil is often used with wipeout. I used to use Sweets alone and had some success with it.

Using a phosphor bronze brush like I do will deteriorate the brush since it's essentially the same thing as the material you're chemically removing from the barrel. Don't be afraid to brush the barrel vigorously.....the bronze brush won't hurt the barrel.