Model 70
You will need to find out what model you have. I know it's a Model 70 but submodel such as Alaskan (Should have 25" barrel), Supergrade (Should have black fore end tip), etc. As stated the 300 win mag wasn't released to the public til 1963. Does your barrel have a rear sight that is dovetailed into the barrel? If the rifle has no sights it definately isn't the factory barrel. I would guess you have a one time Magnum caliber and the rifle was rebarreled to 300 win mag. However, the rifle could have been a standard caliber and a Gunsmith opened up the bolt face to accept 300 win mag. Do not fire but try to chamber a 300 win mag round. This round shouldn't chamber in a 300 H&H chamber.