I don't like posting pictures from books without the permission of the author. But if you look on page 144 "Gunsmiths of Virginia" Martin Sheetz Rifle, compare the engraving on the lid to the one you posted. See page 282 in the second edition of Kindigs, "Thoughts on the Kentucky rifle" . This one was later attributed to Martin Sheetz. Again, the lid engraving is very similar.
http://www.cowanauctions.com/auctions/item.aspx?ItemId=101716Also the Red Patchbox Book page 347,Martin Sheetz , compare the lid engraving.
But all of the piercings reminds me of some of Michaels work. The blank cheek side, seems kind of strange if Martin would have done it. Why would he do such a great patchbox, then forget to carve the gun? Might be a restock, I am just thinking out loud.
Maybe Fullstock longrifle or Homerifle, know.
Thanks for posting the pictures. Would like to know where it is now. Seeing it would be nice.