For black powder/grain of wheat bulb deployment charges these are hard to beat.

Drill a hole in the end, mount the adapted globe, fill with the required amount of black powder, close the cap and you are good to go.

The cap holds the charge of black powder until it is good and ready to pop the cap. This gets around the problem of ejecting unburnt black powder if you don't put enough wadding over the top of the charge.

1.5 mm suits airframes up to about 100 mm in diameter.