I ran across a S&W 681-2 .357 today, and I had some questions about the revolver. It's a stainless 4" model with fixed sights, and it has a square butt, with serial # BAN45**. When was this gun first offered? Was it the predesessor to the 686? The gun is nice a nd tight, and in very good condition. What is the value of the gun? Any information will be greatly appreciated. Thanks!