Diesel fuel to scrub carbon off.
Disassemble gun, let soak in tote of diesel fuel overnight or for a couple hours, scrub off with brass brush.
Scrub barrel out with precision rifle barrel cleaner.
Run patches through until clean, oil barrel with patches.
Grease slide, trigger bar, plunger, inside of firing pin channel, firing pin, hammer spring, hammer spring channel, outside of barrel, inside of slide where barrel rubs.
Oil sear.
Reassemble, shoot gun.
I do this about every 2k.