The gun looks to me to have some similarities to Bull family pices, based on the few guns by them I've seen pictures of. The guard is very unique but has the forward curving spur. The mixed iron and brass hardware, short pointed finial on the entry thimble, the forend shaping, the shape of the patchbox, and the rear sight are similar to some pieces by both Elisha and John Bull. But then again, not exact either. This gun looks later than the John and Elisha Bull pieces I've seen, though.
The small dimensions of the patchbox make me think of the covered grease hole on that nice runsigned ifle in Dennis Glazener's book.
The crisp nose on the comb is different from the John and Elisha Bull pieces I've seen as well, but it is real close to some nice contemporary pieces by Andy Mock shown on Art Riser's website - perhaps Art might know whose style Andy was basing his guns on - are they later Bull guns ?
In any event it is another beauty - thanks for posting!
Guy