The reason to use an expansion chamber is to keep liquid out of the gun. That is all. The advantage of this is that you don't freeze up the 4-way valve and get somewhat improved velocity consistency. This can be much more inexpensively achieved by either running remote, vertical, or anti-siphon bottom-line. The only place I've ever run an expansion chamber on my 'cocker is on the tank end of the remote (Smart Remote) and that only because it was the remote I just happened to own.

In my opinion, with the increasing popularity and decreasing prices of external regulators, expansion chambers are rapidly becoming obsolete. Since WGP started including their own in-line reg with every Autococker from the stock model on up, an expansion chamber on the Autococker has become completely pointless.

Incidentally, if you run both an expansion chamber and an external regulator never put the expansion chamber between the regulator and 'gun. The expansion chamber should always go upstream (closer to the tank) of the regulator. This is because the reg. lets through a certain pressure at which you've chronoed your gun. This pressure of gas would fill the expansion chamber. Under rapid fire conditions the tank chills and the expansion chamber would be filled with cold CO2 to the predetermined pressure. When you stop rapid-firing, this gas will warm up in the expansion chamber and increase in pressure dramatically leading to your next several shots being hot.

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