Cornell Publicaitons has a book on the company that may have sn data.
Harrington and Richardson made it.
Harrington & Richardson did not make a Model 1900. Hopkins and Allen did.
Your harrington and richardson model 900 was made between the years 1962-1973.
2013
There is a company called Harrington and Richardson. They have made shotguns, rifles, revolvers, had military contracts for the M16 and various other weapons. They tend to be functional and basic, not high end.
10-100 USD or so
No where. They went out of business several years ago.
1987
1971
"P" prefix indicates 1953
"BA" prefix indicates 1983
H&R / Harrington & Richardson