The case is a bit of trench art, which we commonly see today as artillery shell cases turned in to lamps and ashtrays and other brass fodder. I have an umbrella stand made of a (I think) French WW1 shell case. I've seen a few engraved cases here and there along the way.
Those grips are interesting. The carving is pretty good for imitating a stag look. Someone with a good eye and some carving skill did those, I'd say. Is the SN of WW1 or WW2 era, or in between them?