Hard to beat guntech's suggestion - then you will know in your rifle. I have 3 M1917's here that were converted to belted magnums - all originally 30-06 chambers in the military barrels. The 308 Norma and the 300 Win Mag both are using absolutely unaltered military magazine boxes, followers and springs. The 300 Weatherby has had some alterations to the military magazine at its rear end to gain internal length, but fits into a WWII arsenal overhaul stock without any additional inletting for that altered mag box, although a minor amount of grinding was required at rear of the action magazine opening to clearance the "new" back end of the box. Two of them have M1917 bolts with faces opened for the magnum sized rim; the 308 Norma has a P14 bolt with minimal alteration. I have no clue how an M1917 mag box dimensions would compare to a pre-64 Win mag box. So far as I can tell, the military feed rails are not touched - would have had to be very subtle, if anything, had been done to them. Certainly nothing like is seen on the feed rails in the BSA conversions of the M1917.
