Yes, that is a 12 gauge shotgun. You remember in the movie he was shooting clay birds when he was interrupted to meet his new scrounger!
My gut is telling my Reagan is holding a Remington 700, no idea on caliber. and wayne is holding a Remingtion 1100 12ga.
The EXIT sign above his head reads the right way so it's not a reversed picture. I'm a lefty too, and I didn't know that about him. Pretty cool !
I think I recall Weatherby gifting their rifles to Presidents years ago. Someone correct me if I'm wrong.