Most of the 1,000 or so G.A.R. halls organized after the war had relic displays. A majority have been disbanded and their relics disbursed. I suspect that was the origin of your shell. I have seen others similarly painted. When I find a photo, I'll post it. I have learned from examining the many painted canteens that a large number of private individuals had small in-house collections. No way to be certain unless others similarly marked turn up on the market. One thing we can say about your fine shell is that it was a common VA style made in late 1862 prior to the requirement of copper fuze plugs in Dec. 1862.
I've included photos of a late war "CS James" (actually a short 3 inch Broun) bearing the markings of the great A. E. Brooks Collection (circa 1890s) followed by MOLLUS (Massachusetts) circa 1900-15.
Woodenhead