I'd first and foremost make sure it's safe, no ignition. Then clean the bore as best you can of rust and crud. Soak it with Kroil or some other penetrating fluid. Buy or make an extractor, looks like a wood screw and thread it into the ball or bullet. I'd use a good stout cleaning rod, you don't want the end to pull out of your ramrod when you tug on that sucker. What kind of nipple arrangement does it have? On a sidelock, you can replace the nipple with zerk fitting and pump grease in there and push the ball out. I don't know if that would be possible on an inline or not. They also make CO2 dischargers that thread into the nipple hole, maybe you could find one that would fit your inline.