Originally Posted by Styrak
[G]as guns are a whole different deal too.
That's certainly true - for AEGs you have a set spring and a set volume, etc. It always pushes the same amount of air at the same pressure when it fires.
GBBs on the other hand have the gas port of the magazine open for as long as it takes for the BB to exit the barrel. (At which point the chamber pressure drops, the shuttle valve flips, and the gas is then 100% directed to slide blowback, at the end of which closes the gas valve.)
How this affects the BB, I haven't been able to test since I haven't had enough gas guns and a chrono together at the same time to do it. I'd love to compare with an NBB (which I think should "act" more like an AEG's spring/cylinder setup.)