Okay, just checked. I don't see anything moving on the bottom of the gun, but I definitly see it through the dust cover. Should the nozzle be perfectly straight? It doesn't seem that way to me.
The nozzle also looks like it's not quite "long" enough. EDIT, nevermind. It looks like this works in REVERSE of the AEG diagram I'm looking at. The nozzle moves forward with every pull of the trigger, rather then in reverse.