The shown "shell case" or "tube" without any visible marks is metallic, magnetic, and shows residue of dark red paint. The base tube measures 50x273 with a 57 mm wide bottom. The tube measures 52,2 mm on the outside, the extending brim at the top measures 55 mm and seems to be the same diameter as the groove at the bottom. The primer is brass, ~10 mm wide and seems very thin.
Any ideas what this could be?
Any ideas what this could be?