British 303 that I was made to believe it was a 308. Stamped on the side of the receiver very small says 308 Italy. However I'm unsure of the barrel that is on there because a 308 fits all the way flush in the chamber to where the extractor can't even grab it to pull it out. It is not a 303, it is not a 308, it's not a 7.62 x 54 and it's not a 410 nor is it 8mm mauser.
To my research it could be a 303/22, 303/25, 6mm Musgrave.
You will have to have a gunsmith figure out the dimensions of the chamber and what caliber it is. I have plenty of other projects and have had this rifle for almost a year and don't see me having time in the near future so it's time to let it go to a new home. $250 call or text 785-259-8140 or message me on here.