Burst charge for paper firefly shells

[yoyo]

Hey,

 

I'm making shells according to http://www.skylighter.com/fireworks/how-to-make/basic-3-inch-plastic-ball-shells.asp, except with paper shells, and just firefly stars.

 

The article says 1.25 oz for the burst charge, but since that's for plastic should the burst charge be lower for paper shells?

 

Also, should the number of pasted layers be lower because the effect is supposed to hang in the sky for a while?

[Xtreme Pyro]

Hey,

 

I'm making shells according to http://www.skylighter.com/fireworks/how-to-make/basic-3-inch-plastic-ball-shells.asp, except with paper shells, and just firefly stars.

 

The article says 1.25 oz for the burst charge, but since that's for plastic should the burst charge be lower for paper shells?

 

Also, should the number of pasted layers be lower because the effect is supposed to hang in the sky for a while?

 

No, the shell should be packed as tight as possible. You don't want your stars moving around in the shell. There is really no reason too weigh out your burst, use some hot bp on ricehulls with a 5:1 BP:Hull ratio and it will suit your needs just fine. Paste 2-3 layers per inch of shell using the 3 strip method, If you are still looking for a bigger spread, either paste a couple extra layers or add a small amount of Vitamin F (~1g).

Edited December 11, 2014 by Xtreme Pyro

[Mumbles]

I'd start with what is recommended there and you can change it up depending on how it works. I've used that method for breaking ball shells before, but never for plastic, and I've never actually weighed the BP. I just fill each hemi about halfway, fill in the spaces with granulated BP, and repeat until full. It works fine on 2" shells, and will probably be the same for 3".

 

At a certain point however, most people will switch bursting methods. Instead of bulk filling with stars, you line the interior of the hemisphere with a layer of stars. This gives a more spherical break as opposed to a ball of color. Additionally as you go larger, it just becomes wasteful and very heavy to bulk fill. You can certainly use this design, and just fill the center with granular BP, but this isn't overly common. This is why most shells starting around 3" and up use milled blackpowder coated onto a carrier (rice hulls, cotton seed, cork, some cereals, etc). This allows you to save on BP and weight of the shell without really affecting performance.

 

As far as the pasting, I'd paste them like normal. The number of layers doesn't affect how long the effect hangs, just how large it bursts. Firefly can look good in both strong and weak bursts depending on how well you make it. I usually use a normal solid burst charge. I think it emphasizes the transition effect more with a bigger cloud of charcoal sparks that sort of get followed by the firefly aluminum sparks. They make fantastic mines too.