Buy a airgun specific bottle, Midland Diving Equipment supply many dealers, http://www.midlanddiving.com/£153.35 for a 3litre 300 bar new bottle and valve.Originally Posted by bmwdick
The adaptor you have will screw directly into the valve assembly on the bottle top, but, it is for a 232bar valve, hence is around 5mm too short for a 300bar bottle.Sandwell Field Sports sell an insert to overcome this problem,which is rather overpriced IMO at around £10.All it is is a small spacer with an o ring on one side.
Dont worry about the 200 bar rating stamped on the adaptor, the gun is filled to 200 bar, you wont be wanting to put it over that, in fact I think there is a valve inside the adaptor that automatically exhausts if the pressure gets too high - there is a vent hole on the side of it.
Alan.