It's the 12 bore frame fitted with a rifled bbl.
Not worth much. You could buy the shotgun version and swap the wood.
Action may need work to lock up right. Probably best as a wall hanger.
Contact:
Seller: Jim Goergen
Company: Goergen's Gun Shop
State: Minnesota
Zip: 55912
Country: United States
Phone:(507) 433-9280
He has 1000s of SS rifles