I remember reading somewhere (probably one of ILLusion's posts) talking about the moving barrel. I believe he was talking about the Airsoft Surgeon barrel that stays stationary...anyway, if memory serves, I remember the gist of it was that the BB doesn't spend enough time in the barrel to be affected by the movement of the barrel. I'll try to track that thread down.
About the KJ M9, I own one and I love it. The mags are leaky, however. I've fixed my mags with teflon tape and generous amounts of silicon oil.
here it is: click
. Check out post #5 & 6