i may sound stupid but o well

[taylor53821]

are a regulator and a expansion chamber the same thing? explains

[camoman5000]

May I lead you to this-

http://www.pbreview.com/forums/showthread.php?s=&threadid=219311

There ya go:tup:

[hybrid-sniper]

Expansion chamber - Allows co2 more time to expand before entering the gun, this in turn decreases the potential of sucking liquid co2 into your gun and velocity spikes.

Regulator - Works somewhat like an expansion chamber, it gives co2 some time to expand, but on top of that it also regulates the air pressure going into the marker, which basically eliminates any velocity spikes.
Note: not all regulators can handle co2.

Bottomline, expansion chambers are pretty much useless today, cept maybe as a trusty foregrip, Anti siphoning your tank is a much better investment.