James J. Grant citations from "Single Shot Rifles Finale"
Page 78 & plates 95 & 96 on page 79. Grant calls this an "H. Larsen" rifle.
Pages 81 & 82: 3 brief paragraphs on a rifle he calls "The Hagen". 4 photos of the Hagen on pages 89 & 90. The final photo shows the action with the side lever & block removed.
It could very well be a Larsen rifle, However it is my understanding that Christiania Norway (now Oslo) had what was like a smaller version of the London gun district. Incorporating over 350 gunmakers from the 1600's to the 1900's. Not to mention importing many guns from Germany and Belgium.
So since it is unmarked I probably will never know for sure.
John