I don't use my GoPro, too bulky looking on the gun or helmet.
I have since switch to Replay. Looks like a flashlight and mounts tighter against the gun or helmet. It is a proven cam although not popular yet in airsoft, but is in all other sports.
http://replayxd.com/
Some airsoft footages with the Replay XD, very natural and not pincustioned like a Contour.
R7 Replay Video Camera: Airsoft Game Footage - YouTube
DesertFox Airsoft: Handgun Operator - YouTube
DesertFox Airsoft: Zero Darkest Thirty - YouTube