Paper cartridge cases were the norm for muzzleloading military arms. One of the first cases for breach loaders, back as early as 1809, by Pauly in France, was of paper. Almost all breach loading shotgun hulls from pinfire to centerfire were of paper. I can't recall when brass shotgun cases were developed but I think it was at the turn of the last century by the US military for use in tropical climes.
Brass cases are neat, but not really PC!