These, and other, flasks, where marked either on the spouts and/or the top flat of the flask beside the spout. Some had panels as part of the decoration that also held a name. True, by the 1870-1880 period there were a lot of cartridge guns around but there were also still a lot of BP shotguns, and some rifles, still being made and used. I think you will find this to be the correct period. I have a number f these flasks in the various variations. Can't post pictures but will take and send them to someone if there is an interest.
Mark