Here's how I clean my shotguns after shooting slugs.
Cleaning shotguns sucks, especially after shooting slugs. Ive had good luck with a bronze brush on a cleaning rod, attached to a hand drill.
The best solvent:
Kroil. But be careful, this is a hazmat nightmare. Figure out how not to inhale the fumes, or spatter lead+solvent everywhere. I use a respirator, disposable gloves, and old clothes.
Instead of cleaning patches, I use paper towels wrapped around a special rod a friend gave me called the
Barrel Wizard. Unfortunately this product is discontinued.
I swab the bore with Kroil, and leave it for ~15 min. Then I scrub with the spinning bronze bore brush, adding more Kroil a few times. Silver colored sludge pours out. I use a box to contain the splatter.
I finish up with more rolled paper towel swabs on the Wizard rod, and then swab with
WeaponShield oil. I also use WS oil to clean and lubricate the action.