I had a neighbor they called YUNK.
Yunk was a old WW I veteran and he had a weapon like that.
He called it his 8mm. He said it like as if it was all one word.
What you have there is probably a WW I army rifle that someone brought home or bought for next to nothing and then spent lot's of time and money to convert to a hunting rifle.
As far as a hunting rifle goes, it was a ok gun.
But nobody ever collected them.
Probably $100 - $1000 depending on who is buying and who is selling. The ammo might be hard to come by if it is a ba$tard round.
That gun is in pretty awesome shape.
Did you by any chance get any ammo to go along with the gun?
Basically it is a Mauser - read the article below.
8mm x 60 Guedes C 0.326 2.35 0.622 0.353 - 0.542 3.23 - -
8mm x 60R Daudeteau C 0.323 2.355 0.627 0.347 - 0.533 - - 1898
8mm x 60R Kropatschek C 0.331 2.335 0.618 0.349 - 0.541 - - 1885
8mm x 60R Rubin C 0.323 2.391 0.558 0.359 - 0.513 - - -
8mm x 60S Magnum C 0.323 2.34 0.468 0.350 0.431 0.470 3.11 .217/5603 1918
8mm x 60RS & R Magnum A 0.323 2.36 0.524 0.345 0.432 0.466 3.20 -
As you can see there are several different chamberings for that designation and you would have to mic the ammo to make sure you got the right ones.