At first glance the gun tends to have percussion era ca. 1840 Lancaster, PA details in the patchbox with detached side leaves with entwined wriggle engraving, relatively straight butt lines, what appears to be a large, round brass patchbox release button in the toe plate, and engraving on the rear pipe and nose cap. The odd inlays tend to muddle the issue, particularly the fleur-de-lis in the butt and the acorn-like finial on the patchbox. It would be helpful to see the tang on this rifle, to see if it is a longer, two screw style tang that might indicate a more southen origin.
Frank Sellers' "American Gunsmiths" has many gunsmiths with first initial "G" and last initial "S." Often when the middle initial is present and first and second initials are "G W" the first and middle names are George Washington ....... The rifle is a nicely made piece, engraving a little simplistic compared to the well cut barrel initials, but well stocked and mounted. There is a chance the fleur-de-lis is significant and the gun might come from an area with French influences, such as Midwestern locations like Vincennes, IN or over in Illinois where French influences were still strong in the late 1700s and early 1800s...or perhaps New Orleans, etc.
Your friend has a nice rifle, the gunsmith obviously made other rifles to develop his skills to this point, so the gun should eventually be identifiable. Does your friend have any family history with the rifle that might help point us in the right direction as to its possible region of origin? Shelby Gallien