That's a nice-looking "conversion" - some are REALLY ugly.

With a number that low, the rifle could have been used in Cuba and/or the Philippines, during the Span-Am War, 1898-1902. In fact, such usage is FAR more likely than WW1 Europe. Your number is not listed in the extant records.

Try and find your relative's unit, from old family records, then see where it served. Google will be a great help, once you get some idea what to search for.