The bolt and trigger group sure look like a Mannlicher-Berthier, although the stock does not look like any of the variants I have pictures of. If it is a Berthier, caliber is 8x50R otherwise known as 8mm Lebel.
Fresh ammo is about a dollar a pop.
I would pass it up. We don't know for sure what it is and if it is the main suspect, it is not a whole lot of gun.