It's on the part of the rotary breech action that the barrel screws into.
I had one a few years ago and can't remember for sure, but it's either on the front side (the side the barrel screws into) or it's under the rotary breech. Slowly open the rotary breech and watch through the loading port and see if it turns by the numbers stamped on the action, if not remove the barreled action from the stock and look on the front side.
Hope this helps!
Slufoot