I am trying to help someone on another board get more information about a double he has. This is his description:

This 1850(s) double rifle along with the Hirschfanger (german hunting sword) came from an estate buy many years ago.

I would appreciate any input....

.62 cal. flat-top octagon steel barrels with deep lands and grooves and a fast twist. (I'm told it requires a special hollow back sabot.????)
Maker... I. Valt: Funk & Sohne in Suhl Germany (a guild gun??)
Only a hand full of flat-tops were ever made.
Features...flip-up rear sights, adj. triggers, large trigger guard (gloved finger)
Stalking Safetys plus two position dolphin hammers, cheek pad, deep engraved furniture, side plates, stock, patch box... roe deer, boar and hunting scenes and gold inlay makers name.
tha rifle has a perfect balance and not front end heavy.

He is interested in history, background, value and loading suggestions. Here are some pictures:

I will give him the link to this thread so he can see if you have any suggestions. I would appreciate any information you can provide.