no difference
Lance, there is no difference between the two.They call it a shotgun scope because of the power.There is no need to put a high power scope on a shotgun because of the limited range a shotgun has.
The scope you are talking about is excellent because if you are hunting in the woods you can turn it down to 1.5 power and still have a large field of view.
I also love the pro diamond reticle.I have a 4x32 pro diamond on my muzzle loader.(wish I would of got the 1.5-5).
Most people would put a 3x9x40 on a 30-30.It'll get you downrange further.
Good luck