Problem Cleaning Bore

You might try JB Bore paste, which is a mild abrasive. The fellow that sold me my jar told me "it will even remove evil spirits"...

I second JB Bore Paste.
It can be bought in many gun shops, or you can order it direct from Brownell's.

This is a super-fine, non-embedding abrasive originally used by benchrest shooters to deep clean a bore.
It won't harm the bore, but will clean it.

Check out the link: http://www.google.com/search?num=20&hl=en&safe=off&rlz=1T4ADBS_en___US205&q=electric+bore+cleaner

You can make a homemade version of the Outers Foul-Out unit very easily and inexpensively. If you're not handy, try sealing the bore with a cork or rubber plug; fill it with something like Shooter's Choice and let it soak for several hours. Drain it, and then hit it with JB Bore Cleaner. Hoppe's is not a very aggressive bore cleaner, and there are much better alternatives available today.

I have a M1903 Springfield that I wore out three brand new bore brushes on, using JB, before it finally came clean. Soaking the bore really helps in these instances.

I cleaned on my grandpa's old Krag for several days with the same results, even tried the "foul-out" rod and came to the conclusion that you'll never get it to where it looks clean. Further, the bore is pitted enough that using the bronze brush was leaving enough copper in the bore that my patches would come out blue again, so I thought it was still dirty. It is as clean as it gets, I'm afraid.

It still shoots surprisingly well so I've given up trying to get it squeaky clean.

Stop up the muzzle, fill the bore with regular solvent and leave for an hour or so. Then dispose of the dirty solvent safely and run a patch through. Repeat the soaking if required. You need to give the solvent time to work. Mind you, some milsurp barrels, especially a 90 year old barrel, will still be black. Eons of corrosively primed ammo.
Brake cleaner is a degreaser. It does nothing for a dirty rifle barrel.

Clean the bore

Are you sure it isn"t rust? If it is try this. You simply pluge the barrel on the chamber end with wood or a cork plug. Mix a solution of 10% Nitric Acid (that's 9 parts water and one part acid). Carefully pour the mix down the bore from the muzzel end until the bore is full. Allow ten minutes to pass. Remove the acid from the bore, remove the plug and flush with water to remove all traces of the acid. Follow this with one clean white patch if there is any rust on it repeat the process. A 10% nitric acid solution will not act fast, (the dilution slows the action). Rust is ferric oxide which is weaker than iron or steel in strength as it is an oxide. So the acid attacks the rust first. It will of course attack the iron or steel but at a later time. That"s why you only allow the ten minutes and is flush with water to remove ALL TRACES of the acid. (CAUTION: DO NOT ALLOW ANY OF THE ACID CONTACT WITH THE BLUEING ON THE BARREL IT WILL REMOVE IT VERY QUICKLY!!!!!!!!!!!)