I used what I could see of the bullet/shot weight and black powder weight. Using FF BP, it seems to be comparable to a HOT 12 gage load. Also, the markings look very much like the Nepalnese markings on the old muskets and rifles being sold now from their armory. It truly fits with a Nepal/Idian/Brit style of 1840's or so. Some of the screw heads look newer and centered, usually hand made screws have the center line off just a little and not as pefectly rounded off as the ones in the pics.
It looks like a Fowling piece for Lords and Officers, although the weight of it totally throws me off, that is close to 38 pounds if you truly mean 16kilo. That sure does seem heavy for a 12 gage no matter how hot the black powder load is or would have been. It does not look that heavy though. There does not seem to be a trindle, trundel or bi-pod attachment. It may have been laid on the shoulder of a hunting assistant and fired that way if it is that heavy. I also notice there are no below the barrel notches or holders for a ram rod.
The rifles and muskets coming out of the Nepal armories, seem to be going for around $600 to $1200 and there are a few shot guns in that mix but nothing that heavy. Those triple circle marks are on some of the muskets, but those muskets are French, Britt and Prussian depending on which Nepal firearm it may be, so it could be an import to Nepal or China mark ?? .
The guy that owns and runs Sportsman Guide in Minnesota is a Nepal firearm nut, maybe he can identify it, he used to have a ton of the firearms for sale. Also Atlantic Cutlery Corp sells the Nepal pieces and maybe they can identify it...
http://www.atlantacutlery.com/p-1566-percussion-hunting-fowler-rifle.aspx
No, it cannot be sold on eBay. To sell on any site other than a chinese site would require a export and import permission, not all that hard to get USA BATFE import approval since it is an antique and black powder, but lord knows China wise what would be required.
I would first look into selling it to a Chinese Museum of some sort, rather than trying to sell it to someone outside of China. I believe if you desire to sell it outside of China, the UK would be your best bet.
If it were me, I would get it ID'd, clean it, oil it and hang it in the home somewhere. It is NOT a WAR firearm. It is a sporting firearm of some sorts for sure.
Hope this helps
Regards
Gringo Grande -
P.S. I personally am not for a one world, one dream, I enjoy my country, the USA just the way it is minus the liberals and dems.