K279907 and K280046 were both shipped in Nov. 1956, so your gun was probably shipped about then, however with S&Ws nothing is ever sure and a factroy letter is the only way to tell when a gun left S&W, unless the number is open on the books, which means the gun left via methods not recorded as shipped to a distributor, such as gift from S&W, loan to a writer or exhibitor, salesman's sample, or out the back door, etc.