Hi
I would be surprised if your cam snapped because you used a windy gun. what normal happens to the right hand side cam is the large washer that sits behind the nut is not properly located, as you can see from the photo the cam sprocket has a recess and the cam nut can be tightened up with the washer not located in the recess. This puts a shearing force onto the end of the cam and the result is a snapped cam. Its always important to ensure the washer is correctly located. HTH.
Regards John