I've picked up a Harrington & Richardson single shot, break top shot gun from my grandfather. I'm having a hard time finding any information about it online. On the left side of the gun, there appears to be a date of May 14, 1921 (or 1951), but the writing is worn so its difficult to tell. I've attached a few pictures. Can anyone tell me the age of the gun and how much its worth (ball park)?