Gonna take a guess at CO2 ???
there are a few ways to reduce CO2's
there is a valve mod to blow more air to blowback and not to bb
a refillable CO2 bulb that you fill with Green Gas
or mod the hammer to not fully depress the valve and reduce the burst of air - (risky on a decent pistol)
Even then some sites demand you chrono on a fresh co2 bulb as the first few shots can be way over
my own Co2 would hit well over 500 then settle to say around 425fps until nearing the end
Luckily on my cheapo non-blowback Co2 pistol I managed to source cheap Green Gas mags for it and finally got to use it within the limits
