I was just given what was my grandfather's S+W K-frame .22 revolver, which I believe he got in the 40's or 50's. Its serial number is K56xxx, and I was told that these first three characters of the serial number can be used to approximate the age of a S+W "if you have the right book". I don't. It's in beautiful shape - hoping to get out to the range and put some rounds through it soon. Anyone got any ideas? Thanks.