AmBraCol
You want the coarsest grain powder you can get
Monday, September 20, 2021, 08:03

You want as slow of a burn as you can get to keep from shattering your pay load.

As kids growing up in the Amazon Basin, we had access to all kinds of great fireworks of the launch and BLAMO type. Nothing fancy with starbursts and such, but plenty of fooopBOOM stuff. One year my cousin and I decided to celebrate the US Independence Day in style by taking a half dozen of the "morteros", as they were called, and combining them into one. We got the single BANG type instead of the triples as we reasoned we'd get more of the pay load powder that way. We carefully rolled a new tube out of heavy paper using a piece of pipe as a mandrel. We used another pipe to form the pay load tube and fitted it with the same fuse as one of the standard morteros. We looked over the arrangement of the original launch tube and our own reinforced tube and decided half the total launch load was about right. All things assembled, we were ready for Independence Day.

That year Independence Day fell on a Sunday - and our families were always busy on a Sunday. We got back to the house about 9 p.m., well after dark and all the neighbors are already in bed (thankfully we lived on the edge of town so none were too close to us). but our folks said it was too late for fireworks. Is it OK if we just shoot off ONE? we inquired. Receiving permission for ONE was received, the parents somehow not having been informed of the nature of The One we planned to launch.

We set it up out in front of the house in our volleyball court, which is now a street, and rigged up a fuse to reach the fuse by chaining together the combined fuses of some of the morteros we'd dissected to build the new one with. They were rolled in toilet paper and there was a bit of paper at the lighting end to give it a bit of a burn before reaching the fuse proper. So we lit the fuse and skedaddled to a safe distance. We saw the weak flame of the burning toilet paper reach the tip of the fuse chain which began to burn more quickly up until it reached the touch hole in the launch tube.

FWHOOOOP!!!! went the launch charge and the pay load went whizzing up into the air trailing sparks from the lit fuse. It sailed up about two or three times higher than the usual mortero would and then WHOOOOOMMMM!!!!! went the payload. It rattled every window in the house and woke the neighbors, who had NO idea what was going on. In those pre-telephone, pre-electricity days no one called the authorities and we felt justified in interrupting their sleep as they had no qualms about throwing all night parties that wouldn't let US sleep far more frequently than we ever celebrated Independence day.

j
Anyway, back to the theme of your experiments - you want a smaller charge of slower burning powder. If you can source Fg it'd be a good one to try. The launch charge we used in that one I told about was composed of a VERY coarse (about lentil sized kernels) slow burning powder. To use standard firearm powder I'd start about 15 - 20 grains and try it with a dummy payload first.

Another thing we learned from our experiments was the effect of tightly wrapping smaller charges of fast powder (firecracker powder) to get a bigger BANG for our buck. Key to getting this to work is to wrap it in such a way that it can't simply blow out one end like a cork out of a bottle. We would build up layers of heavy wrapping paper (remember when packages were wrapped instead of dumped in a paper or plastic bag?) and glue and let it dry thoroughly prior to use.