It's easy to remove corrosion from the male side of bullet connectors, but the female side has always frustrated me. Stumbled on by far the best tool I have found for this. A small bore .17 caliber brass rifle cleaning brush avaiable for a few bucks at sporting goods stores has a tapered end small enough to get the brass bristles all the way into the female connector. Some finger rotation of the brush and you're quickly down to clean bare metal. Plug it back into the emery cleaned male end and the connection will be primo again.