If 4K is an overkill when taking footages of the airsoft action, you can always go for the Runcam Scopecam Lite which does 1080p video. It has a standard mounting system allows you to attach it on basically any gun firmly and can be easly installed and detached. Battery is also rechargeable. Maniek44 got a unit to review to find if it is something he can recommend to airsoft players.