I have looked for information. Didn't find a lot, but here it is.
Tennstempelrifles were used for both target shooting and hunting in Norway, by those who could afford them. They were expensive, I found a reference to an 1880 price list. The price of the cheapest tennstempelrifle was 2 1/2 times that of a Remington rolling block. The most expensive tennstempelrifle cost half again as much as that.
The rifles appear to have been quite popular among sealers, who both made a lot of money and would have considered a good rifle an investment, since their pay was directly tied to how many seal skins they brought back. Sealing involved shooting off hand standing in a small rowing boat in the open Arctic Ocean. A seal's head is a pretty small target, often shot at ranges of well over 100 meters with open sights and black powder trajectories, so these men would certainly appreciate a good rifle.
The rifles were as mentioned in my previous post designed by gunsmith Hans Larsen of Drammen. He held patents until 1886, but he did sell receivers to other gunsmiths who then added their own barrels and furniture. After 1886 L.H. Hagen made his own version of the rifle. Although Jim Keenan is right about Oslo's old name, it really doesn't help dating the rifle. The Norwegian government started referring to the city as Kristiania in 1877 (not '78), the municipality itself stayed with Christiania until 1897. I have no idea which spelling gunsmith Hagen preferred. And one thing I failed to mention in the first post: Staal is not a part of the name, it's simply the Norwegian word for steel (spelled stål in modern Norwegian). All rifles were of course made from steel, so I would guess the word indicates some level of "quality" steel, but I don't know.
Caliber could be anything from 12.17mm Norwegian ordnance to a number of the English black powder "express" calibers popular at the time. I think some may even have been made in smokeless chamberings such as 8mm Danish and 6.5x55. Maybe.
I found a couple of references to auctions that indicate that a tennstempelrifle in decent condition goes for something around $1500 in Norway. But I'm not a collector and have no idea how well this reflects the market, the price will of course also depend on model variations as well as condition. Besides, it's only worth as much as someone is willing to pay for it - you probably won't find hordes of American collectors fighting each other over something few people outside of Norway have ever heard of. I have never handled one myself, although I've seen the odd one in museums and such.
Hope this helps.
