Smith and Wesson .45 Hand Ejector U.S. Service Model of 1917. Serial number is 163063. My money is that it's a 1919 but any help that anybody could provide would be greatly appreciated.
According to Roy Jinks, this model had its own serial number range commencing with #1 made on September 6, 1917. He states factory records indicate they had reached S/N 163476 when the war ended Nov 11, 1918.
This would make yours one of the last produced during the war. Many of the later-production revolvers were not delivered to the U.S. military as they were no longer needed and were sold commercially, the last of the wartime production leaving the factory on January 5, 1921. After this date production of the model for commercial sale continued (with checkered walnut grips) though sales were at a fairly slow pace.
From "A History of Smith & Wesson" by Roy G. Jinks