R.Marshall,
Reading the serial number as 868( can you verify it is not 368), Axel dated the action as 1898-99. If it were chambered for 6.5x57 or 6.5x58 Port., it should not chamber a 6.5x55 Swed. original specification cartridge, because it had a larger diameter case head. American 6.5x55 ammo is often( if not usually) in cases with 06 head size cases so if you tried an American cartridge the test might not work. Mauser knew of the 6.5x55 and had the reamers because they developed the rifles for the Swedes, but the rifle was barreled in Suhl, rather than Oberndorf. If you used an American cartridge, a chamber cast might still be advisable.
Mike
