The inside diameter of soda bottle necks may vary to some degree causing them to fit differently on the launcher core. If you experience excessive leaking and loss of pressure, try switching to a different soda bottle - this might solve the problem. If it doesn't, you may consider using a slightly larger O-ring than that provided as standard equipment on your launcher. Try using 1.6mm, 1.8mm or 2.0mm O-rings for increasingly tighter fits. These are generally available at local hardware stores, or if you prefer, you can order them directly from us (see our components page).