The original drawing comes from "Aide-Mémoire d'Artillerie Navale. Planches. 3e Livraison 1878, chapitre 1-Bouches à feu" ("Notes on Naval Artillery. Drawings. 3rd Edition 1878, chapter 1-Ordnance"). Unfortunately, it's not available online and the actual posted image comes from this thread, in French.Sorry I can't remember where I found this drawing. I have it in my files as 37mm Model 1877 (without crimp groove).
I just found this one on the internet (same early Hotchkiss Mle 1877).