Hey August,
You might want to get on a Mauser-centric website and see if somebody has a reference book with serial #s. Given that yours is a sporting rifle (from what I can see) and has the switchable barrel feature (something I'm not familiar with), you might need a "Mauser guy" to hunt it down. Do you know when your dad got the gun? They stopped making rifles (I think) in the 90's. The action is legendary and it's tough to establish the value with what I've seen. I don't have a Blue Book, but many people do (your gun dealer will too, but you have to be careful there)and it may be more straightforward to get a ballpark value that way.
Just looking on GunBroker, the floor for this gun should be $500 but, if it's a rare model, it could be worth several thousand. I don't think it's a $15,000 rifle from the looks of it, but that's all out of my league!
JJ
