I recently installed this on my Piranha STS G2. The expansion chamber works as advertised by keeping liquid CO2 out of the gun. However, just to be safe, if you're shooting CO2, don't point your gun toward the ground. This allows CO2 to flow into the expansion chamber and could cause some serious velocity spikes. Because the chamber provides extra space for CO2 to convert to a gas, it allows for more consistent velocity. Since I've added the chamber, I've noticed that my velocity spikes range about + or - 5 FPS. Before I put it on, they ranged + or - 15 or more FPS.
ACI does not provide instructions for installing the chamber. It's obvious that it screws into the vertical ASA, but there should be something to explain how to loosen the chamber housing. You have to do this in order to properly run a bottom line to it. As explained in an earlier review, an allen screw at the bottom of the chamber has to be loosened. I had to call ACI and get one of their reps to tell me how to do it. Then, after he explained it, I slapped myself because it was so easy.
I got the chamber for about $40. It was the best price on the Internet. As stated above, it works just like advertised. If you shoot CO2, this is a good upgrade, especially if you don't plan on changing to an HPA tank or converting to low pressure.
9 out of 10
Last edited on Saturday, January 29th, 2005 at 7:33 am PST