Welcome to the Forum. I just picked up a 38 Hand Ejector (M&P) Target, 4th Change with #281785. It was shipped in August 1917.
Just checked the database and find that all 1917 listed ship dates occurred between 255,XXX and 288,XXX. So 90% chance it shipped in 1917 and a 10% chance it shipped in 1918.
Let me add that the 38 Hand Ejector was manufactured, starting in 1899. Many changes occurred in the manufacture of this model and each major change was identified as a grouping of gun serial numbers. Your revolver was part of a huge production effort, a half-million plus revolvers, that lasted from about 1915 to 1942. They were called 38 Hand Ejector (Military & Police), 4th Change. Started with serial number 241,701 and continued until WWII production started around 1940-1942.