Serail number and features
IIRC, Cornell Publications might have a book that can help
About 1973
Harrington & Richardson did not make a Model 1900. Hopkins and Allen did.
Harrington & Richardson used the Prefix AT in 1983.
Your harrington and richardson model 900 was made between the years 1962-1973.
I purchased a new Harrington & Richardson 12 gauge model 088 from K-Mart in 1980.
More information needed to determine model of firearm.
between 1949 and 1952
25-100
10-110 usd
2013
1871