a regulator will do the same thing as an expansion chamber in the effect that the co2 has to pass through the area of the regulator, allowing the gas to expand sort of like an expansion chamber would, but using an expansion chamber would not be a good idea if you're using nitro, as i think it restricts the flow of the nitro gas?? not sure on that one, but overall a regulator is much better, and is able to be used on most any gun, now or in the future if you would decide to purchase a new marker... expansion chambers are ok, but if u have the money, go for a reg.....