hi guys pistol arrived yesterday with a co2 cartridge in.had great fun with it in afternoon.loaded another co2 cartridge another string of shots brilliant.left it overnight.put a cartridge in today and could hear gas escaping.emptied the cartridge.put another in nice and tight same again.should there be a visible o ring seal where the pin punctures the cartridge?i cant see one.is there a procedure to loading the gas?i had a beretta a while ago and loaded it the same as i did that.any help much appreciated.thanks