Once you have gotten it as clean as you can with the methods you described, which are not too bad a way to clean a ML (I prefer boiling water, but that's from habit), use some JB Bore Compound in it according to the directions! I got ALL the rust out of a badly rusted flintlock bore once using JB, but I had to scrub for about 15 minutes to do it!

Like the rest of you I use the hot soapy water with a bore brush and then a 12 gauge bore sponge like thing, actually is like heavy cotten. when done sloshing up and down I,as learned in basic training, take the rifle into the shower and rinse with as hot as I can stand water. this really finishes off the process than a traditions pre buttered swab. Love those pre buttered cotton discs ( Swabs). they come 100 to a jar and are great for cleaning between shots also.