I got this news just now from
http://www.airsoft-news.eu
Here's a link to the two videos of both guns shooting in GBB. I did not see any external gas can, I think everything is built in.
http://www.taniokoba.co.jp/toygun5min.html
It reminds me of the Madbull's concept of Airsoft GBB Gearbox for armalites. They lost a lot of money making it though.
EDIT: I just realized Tanio Koba described the C8 as M4A1... so it's a M4A1 not a C8!!! I got C8 off airsoft-news.eu ...