About 1973
That should be 1975
Serail number and features
what letter or letters are in front of serial number
No way to tell.
"AD" prefix indicates 1967
M prefix to serial # = 1952 manufacture. Jim
"AX" prefix indicates 1981
Seldom exceed 75 USD
The prefix letter shows the year of manufacture. 1956 is letter S
More information needed to determine model of firearm.
Seldom exceed 100 USD
Harrington & Richardson used the Prefix AT in 1983.