Try using a oversized bore mop to fit the chamber snug... with 91% alcohol -or- lighter fluid -or- brake cleaner (non-chlorinated). Soak it pretty good, insert, twist, etc. Then let it sit. Take it out and wring it dry, towel dry, etc. Do it again. When you're satisfied, use a clean bore mop to remove any excess and dry it.
This, only soak the bore mop with Kroil oil, using a pistol rod insert into the chamber, the bore mop should be left in the the chamber for a couple of hours. If you want you can mix the kroil with a solvent like trying to clean Moly, but would not use a high ammonia type. Kroil is a penetrating oil that will not dry out and dissipate like alcohol or lighter fluid.
After soaking use a pistol brush that fits the chamber and spin it to break all of the crud loose, swab out and lightly oil.
