I bet a PTW barrel would be a very close matchup.
Coach...that black cage thingy that the guy put on the barrel is the roller cage. There's two little rubber bumpers that push it down onto the BB as it passes through.
The allen screw he puts into it before he puts on the outer barrel pushes the cage up from the bottom and causes it to put less hopup on the shot. Screw in = raise cage...unscrew = more hop.
I'm freaking tempted to buy an AEG M4 just to try this out...