Hi gang, I hunt and have rifles and shotguns, but I also have a S&W .357 Magnum 681 that my father had owned. How do I find out the year it was made? Top part is stamped MOD 681 and lower says (it's either an O or a G) G18 and stamped under it is ###X# (three numbers, an X, another number). Any input would be great, thanks!!! TB