It was BEH. The paperwork I had said REH, but it was a typo. The gun is stamped BEH. Thanks for the info. It is a 686-3.I can tell you that the 686 was introduced in 1980, but I couldn't find the serial number prefix "REH" listed in my copy of "Standard Catalog of Smith & Wesson".
Are you sure it's not "BEH"? If so, that would be Sept. 1989.
If that's wrong, don't feel bad, I myself have two S&W's that I can't find in the book either. One is a 3" M#629-5 "Mountain Backpacker", serial number prefix "MBP", and the other is a 6" M#29-6, prefix "SBR".
If you can give more info, I can narrow it down by features and production changes. Is it a 686 no-dash? if so, those were made from 1980-85. If the model number has a "-1" , that's a 1986 production gun. The dash numbers go up to 5, with -5 being 1998 to present.