Well I tried my hand at a more traditional moose call. the plastic bleach jug was bringing down my hunting party...lol
Here is what I did and learned:
found a good piece of birch sleeve, thick, few knots, and bark slits. I cut out piece with utility knife and used some boiling water and a chisel (mallet when need to remove the sleeve. slow and easy trying to stay in cambium.
Cut out a template using flexible cardboard, so I could roll, getting a feeling of dimensions (shape and size)
Used the template to cut out sleeve, made some little adjustments (moved all to template as I went, so I could replicate if I had too. (was my first attempt) lol Note: natural curl of birch is having the inside bark out, so I used this in my build.
Got cut out sleeve and other materials ready for soaking, not sure if this was the best, but worked once dry (but made sleeve very brittle when dried, might just rub down with oil next time.