The worst thing to do is fire up a charge under a ball stuck half way up the barrel. Doing could bulge a barrel. In your circumstance the grease pump method is most effective verses a CO2 Discharger. The co2 deal works best when the ball is fully seated to its breech on top or not its powder charge. The ball gap you your rifle has its likely the co-2 cartridge wouldn't have enough pressure filling the gap and pushing the ball forward. Keep in mind your rifle nipple is Metric measured thus the grease fitting needs to have the same threading and profile look. Good Luck,