Dischargers, smoke generator, 4 inch

[wheaty]

Blanks had many forms, but you are correct in that most launching rounds did have a rolled crimp and wad.
Some blanks had a roll crimp and wad, short crimp, full bullet length crimp and of course the wooden bullet blank.
Many of the "blanks" around and especially if WW I dated are mortar igniter rounds and do look like blanks but are for use in large mortars and some naval guns.