Welcome to the forums from the Wiregrass! As Jonesy says, that's a WWII Victory service revolver from 1943. It has been refinished at some point in its life. Take off the grips and see if the numbers stamped on the back of the right panel match those on the butt of the gun. If so, the grips are original to the gun. S&W made about a million of these and the British Service Revolvers during WWII so they aren't rare or bring high values unless they are like new in box. But, that doesn't mean much to you as your gun is an heirloom from your Grandfather and is thus priceless. Congratulations on a fine inheritance!