This is an excellent illustration of the tin (tinned iron) drum canteen built with one particular side flat and the other convex. In this instance the convex side has yet another stage up, making it only a tad more… https://rajanmstm765898.isblog.net/the-5-second-trick-for-the-wyatt-canteen-non-fringe-a-haute-southern-hyde-45936817