Yeah,
I'd split the composition as well. A separate shot of the dog at an ideal angle, and same for the gun. Perhaps both on the same white background so they can be photoshopped into the same frame easily.
You might want to make it a handgun, perhaps a nice PC-looking revolver, although a pump 12ga is also about the most PC as it has heavy sporting and rural connotations as well. It's just that as you probably know, and much better than I, long guns are difficult to frame properly in their entirety.