Serial# BLK18XX would date to the early 90's, probably 1992ish.
BUT, there is a problem. You say the revolver is a Model 17-4. The -4 production and engineering change occurred in 1977 and was followed by the -5 production and engineering change in 1988, and the -6 production and engineering change in 1990. SO, something is not right in Nevada. The revolver can't be a -4. The serial# is located on the bottom of the grip frame (butt) and you may have to remove the grips (if it has target stocks) to see it. Report back and someone will help you out.