I concur...leave it completely alone! It is not deteriorated or coming apart and the metal in in terrific shape. I'd say the rifle is from the first quarter of the 19th century, and is in the style of Deringer and a few others. It's been converted to percussion and about 14 - 16" of barrel and forearm have been bobbed.
In the past, many rifles such as this were completely restored - barrel 'stretched', new forearm, re-convertion made. I think a lot of the rifles that have been published fall into that category. If you decide to go that route, research carefully who would be the best artisan to do the work, and be prepared to invest a large sum of $.
Do not attempt the work yourself...you'll destroy the rifle. I say that without the slightest notion of your ability, skill, or knowledge, and do not to intend to demean any of that.
And thank you for showing it to us.