I have found that you can clean a nasty bore quite well with a patch of 3M Scotch Brite scouring pad on an undersized jag. You will need a lubricant of some kind on your Scotch Brite pad. I found that soapy water works quite well. Just run the Scotch Brite pad down the bore and start scrubbing using full length strokes. Don't use short strokes in one place because you want to make the bore the same its full length.
You can also use some steel wool wrapped around an undersized bore brush. Just make sure that the brush is undersized so it doesn't get stuck. Use the same full length stroke technique as with the Scotch Brite. Make sure that you are using a lubricant such as soapy water or even some oil.
In either case, you can often feel the bore crud being scrubbed loose. It usually takes anywhere from several strokes to a bunch of strokes, depending on how badly the rust and crud is built up in the bore, to get the offending stuff out. Use a bore light to check from time to time.
If you use soapy water as your lubricant, be sure to thoroughly rinse and dry the bore when you are done. I have found that several dry patches followed by spraying some WD40 down the bore gets out the final traces of water. Then just wipe out all of the WD40 and apply a good gun oil.
You can remove rust from the outside of the barrel using 4-0 steel wool with oil. I have found that motor oil is the best. Do not scrub, just gently rub until the rust has been removed. 4-0 steel wool with an oil lubricant will not harm the bluing unless you try going King Kong on it and scrubbing too hard. Rub gently and the rust will come off. Once you have it off, you can use some cold blue, if your barrel is blued, to touch up the spots where the rust was. If you have a browned barrel, the rust won't make any difference so just buff it with the 4-0 steel wool and motor oil to even out the rust spots.
If the stock needs attention, that is another process. If that is the case, just post your questions about how to repair your stock finish. We'll be glad to help you on that, too, if you need it. :thumbsup: