Remove the bolt from the receiver and take a pic. The pics you posted don't tell us much except that it was built on a military Mauser action. You should really have a chamber cast made to identify what cartridge the barrel is chambered for. Lots of confusing info there. The ".22 Zipper" is some unknown cartridge. There is an old cartridge known as the ".219 Zipper", but it's a rimmed cartridge. The ".22-3000" is simply the .250-3000 Savage necked down to .22. And then, the barrel is stamped ".22-250 Improved", which is an Ackley Improved .22-250 that's still popular today. Chamber cast and head space gauge time! And, being it was "Grandpas'", I'd probably set it aside and not shoot it much if at all. . They don't build rifles like that one much, anymore.