Rifles and shotguns made before the 1968 Gun Control Act became law were not required to have a serial number. Yes, it is perfectly legal to own a gun that never had a serial number. It is, however, VERY illegal to REMOVE a serial number.
"P" prefix indicates 1953
Harrington & Richardson used the Prefix AT in 1983.
1973
How old is my Topper 88 HARRINGTON AND RICHARDSON GUN serial number
Cornell Publications may have a book on H&R history
1987
May not be marked, depending on age.
1971
Serail number and features
1980
The value of a Harrington and Richardson 7mm Remington mag serial number 52897 depends on its condition. This gun in excellent condition is valued between 125.00 and 200.00 as of 2014.
No way to value with just the serial number and no other details