Shotgun from Movie version of Little House on the Prairie

I did a search, but found nothing, so...
What was the side by side shotgun used by the dad (Charles Ingalls) in the newer (2005) movie version of Little House on the Prairie?
It was odd, the right barrel was a 12 gauge, but the left barrel was 410.
????
Never heard or seen anything like it. Was it historicly accurate for the period? the rest of the props and such seemed accurate.
I am wondering why such a thing would be built.
Tried to do a screen grab, but I need better software.
Thanks for any help you all can offer.

MAV