I mentioned the CO2 units a few posts back, but maybe it bears mentioning that you can get adapters so that they slip over common cap sizes (with a little o-ring to get a good seal) and they also have a rubber cone-shaped affair that you could jam into pretty much any hole. You just put the cylinder into the unit, screw on an adapter, attach it to the gun, and pull the trigger on the CO2 unit. The ball will fly out with considerable force so do be thoughtful about where you point it. The whole unit and some extra cylinders zips into a bag maybe the size of my fist so you can throw it into your range bag and forget about it until you need it.