Need to find some info for a friend

[johnnyh]

A friend has a Hopkins & Allen, single shot 12ga. It has an exposed hammer and is not a "Forehand" model.
The serial number seems to read 16111. I am trying to find info on this maker of shotguns (a website or a book would be great). I am also looking to find out what the little lever is on the side.

 

[ACP230]

The lever might be a takedown pin.
My grandpa's old single barrel had a pin that looked a bit like a lever on the side.
Loosening it and unscrewing it allowed the gun to be broken down.

Old Sears or Wards catalogs might be a good place to look for info on an old shotgun.