Incised carving requires as much or more skill than relief so you may decide to leave it plain or do relief carving.
Shumway illustrated a very plain early Lancaster rifle in Muzzle Blasts long ago. It had a daisy patchbox but otherwise would be a good model for an uncarved rifle. He thought is was Rev War era but others think 1780's-1790's. If you email me I can scan the article and send it to you.
rpierce@dom.wustl.edu