Does anyone know what this is? It’s a light-alloy tube, 127mm (5 inches) long with an external diameter of about 21mm. One end is closed, with a rim and a small primer, the other end is open and sealed with some glossy black substance.
There’s no headstamp but very faint stencilling on the side, which reads (among other things) M 39 BLAST TYPE 5 and FEDERAL (something) PITTSBURGH. It also says USE BEFORE APRIL 1950.