Impossible to answer without the serial number.
@ 1993
No way to know without the serial number.
1979
@ 1978/9
74
Thew old model 66 was made between 1983 to 1988. after that the model 66Rt was made from 1993 -1994 the model 66BX was made up to 2005 and the new 66 powermaster is new for 2012
Without providing the serial number there is no way to tell. The Model 66 began production in 1971. Call S&W with the serial number and they will tell you when it left the factory.
1980
A Smith & Wesson model 66-1 with a serial number 36k7162 was made between 1990 and 2000. The exact date of manufacture can be determined by contacting S&W to have them look it up.
serial number 514X9
By the serial number letter prefix. The Model 30 was introduced in 1964. A Y or Z prefix is for 1964. AA in 1965, AB in 66, etc.