Is there any technical documentation (manuals?) available on Belgian 25mm (cal4) flare cartridges as they were made/used between 1918 and 1940?
The Belgian types are quite distinct as the brass cases do consist of a very thin brass body (the outer case so to say) with a cardboard liner (cylindrical portion and the insde of the head like with cardboard shotshell cases).
So the cases are basically like a cardboard case with a stamped metal head which is reaching all way up to the case mouth. The cardboard is basically invisible when looking at a loaded cartridge. Just when they get handled one will notice that they are considerably lighter than fully drawn (regular) brass cases will feel like.
Any help is much appreciated.
Here an image for reference showing some of the known variations: