Gavins, this was not a dumb question at all. But as a gunsmith of over 30 years experience, the best thing to do with ANY rifle (or handgun), of which you are not familiar, is to take it to a gunsmith before doing anything with it. There were so many sporterized military rifles that were altered (they cost only a few dollars back then), that you cannot be certain what was or was not done to that rifle. Because caliber is not your only concern. You also need to know if the head space (the correct pressure against the cartridge inside the chamber when the bolt is closed), is correct for the cartridge it actually fires. Improper head space can result in massive over pressures against the bolt's locking lugs, causing a possible blow out (as well as myriad other nastiness).

Hope this helps