I have one of these old Hopkins & Allen shotguns in 12 gauge and I thought I had some information on it but can't locate anything. If I remember it cost me about $200, 10 years ago and is only in fair condition.
I am not impressed with the strength of the action and the system for holding the barrel onto the action seems a bit flimsy. I would only shoot it with modest blackpowder loads.
Sorry I can't be of more help.

OK, I found something on the Hopkins & Allen shotgun. It was advertised in the 1895 Montgomery Ward catalogue. Cost was $6.50 in 12 gauge, $6.45 in 16 gauge and 5 cents less in 20 gauge.
The advertising copy says in part; "One of the strongest and best made guns in the market. The H&A gun never gets loose and shaky in the hinge joints like the 'tip up'barrel guns, as it has no joints and the barrel does not 'tip up'but is firmly fastened in the breech action."
This information from " Rare Selections From Old Gun Catalogues 1880-1920," published by Gun Digest.