A very pretty rifle and in good condition. Thank you for bringing it to our attention. In looking at the photos, I don't see a strong association with Joseph Hillegas, however. To my eye, it looks more like a possible Harrisburg gun, with the patchbox style, and the checkered wrist. Sellars lists two 'J.H.' makers, and others with three initials beginning with 'J' and ending with 'H.' He doesn't say more than that; too bad!
I own a J. Hillegas swivel breech, a fine one, and the name is on the top barrel in stamped letters. There is no similarity between these two rifles that comes to mind.
A good example of a Hillegas rifle is shown on page 150 in the book Kentucky Rifles and Pistols, 1750-1850. That gun pretty much typifies the style and work of Hillegas, particularly with regard to the patchbox style, architecture, and triggerguard. Thanks again.
Dick