Coleman changed the bottle a while back (before I got my first GBBR). The newer bottles can't be refilled (unless you'll going to alter them).Propane is absolutely the way forward for gas guns, yes it's not as clean as say abbey predator or whatever... but if you refill coleman canisters from a big 20Kg tank then the gas is effectively free. When I had the tank/adapter it was costing me way less than £1 for a full coleman sized bottle of propane.
As to the question from another post of FPS propane v green gas - it's the same ...