I'm having wonderful success using my Defender this IB. Lots of noobs running in only to get a shotty or sword in the gut. The kill in this clip is hard to catch but a guy trying to rocket me from the waterfall blows himself up and I get the kill. First time I've ever used my Bubble specifically as a weapon :)

http://xboxdvr.com/gamer/red%20robber/video/12262901

It once got me a double kill in the heavy ammo round just like you got!