We have discussed this gun a number of times here - as Rich pointed out it is a really neat rifle and very unique. The condition of it is really amazing - one of the most pristine iron mounted guns I have seen.
just my opinion but I would tend to guess this gun to be somewhere in the late 1790s-1805 era based solely on the lock. Were it not for the lock I would have no hesitation believing it to be a 1790 gun or a even few years earlier. A lock like this could have been on a high-end English gun by the 1780s, but its use on an American rifle like this would not be something you would expect before the mid 1790s. Others may have different opinions but I think that the buttplate has a very early look - in side profile it calls to mind the Tileston rifle a bit. It is rather compact and the sides much more convex in cross section than you see on iron guards even on most other 1790s iron mounted guns from SW VIrginia and North Carolina (not that we have a ton of those to study, but there are a few), retaining an early feel.
Dennis - the photos on the blog did not show the underside of the guard - I seem to recall trading some e-mails with you a couple of years ago - I do not have much knowledge of military muskets of the era but the guard did not exactly resemble any of the styles I am familiar with - I tend to think this guard could actually have been made to go with the rifle, rather than being cut down, but I don't know.
It definitely is an all business gun -I could easily see someone toting around something like this right at the end of the era of Chickamauga Wars. Looks like it was made to stand up to hard use. Maybe even someone who had some training at one of armories of the era or maybe even as a prototype for a militia contract rifle.
Guy