Here is "Plan B", from beginning to end:
The raw material... somewhat tight fitting cardboard tubes - check the pyrotechnics vendors for tubes that you might be able to use.
Cut them. Power saw worked nicely, just go slow. You can cut both the inner and outer at the same time if your particular needed sizes are the same as mine were. I was starting with a couple of 3 inch pieces and needed a couple of 2's and a couple of 1's
After cutting, this is what I had
They didn't fit as tightly as I wanted, so I glued a layer of drywall tape in the inner cardboard where the slip-fit joint would occur.
End plugs sized to fit the inner piece of cardboard (from same pyro dealer as the cardboard tubes). Also some colored cardboard to cover teh ends. The orange is a "color code" for a blank charge, and it gets glued on so that it is visable on the cover.
Goop some glue on the end...
And stick it to the colored paper. This is the "bottom half" so the colored side of the paper is not going to show when it is finished.
Glue an end-disk into the bottom of the can-half. Use lots of glue here.
The bottom half got a long inner and a short outer piece of cardboard tubing. Repeat the process to make teh top half with a short inner and a long outer
The I put the color coded side face down and spraypainted it with flat black spraypaint
In goes a charge
And on goes the cover
The first one was a bit tricky, but they are getting easier. It only takes about 5 minutes apiece in batches of 4 once you get the hang of it.