Appears to have started life as a British Pattern 1914 (or just plain P14) in .303 British caliber, or a US M1917, in which case it would've originally been in 30'06. What are the receiver ring markings on your rifle?
Just guessing, I betcha it is a converted 303, that is, converted from a valueless P14 to a very nice and valuable hunting rifle. Hey, at the time it was a very cheap surplus " Brit " rifle. I doubt if it was a 303 converted to .308, Of course it could be a reworked Model 17 in 30-06. Brother Wolf, please get back to us with more information. You can't leave us hanging like this.