comet bomb cakes

[DanielC]

I was looking through my workbook last week and found an old article from PF on bombettes. I have built many bombettes for cakes in the past, but at the end of the article it had a section on comet bombs. Basically, it had no fusing or clay double bulkheads. On one end it had about a half inch plug of some random star/comet comp and the other end a strong plug was glued in. The middle section has the effect stars and burst. I was thinking about how simple the design was and how much easier it would be to make a batch of these versus bombettes. I built a dozen or so to test just to see how well it worked. The problem I was having is that the comet plug was not burning evenly and some of the breaks seemed like it burned through on the edge of the casing or just a pinhole and would just ignite the burst and stars and just spray out the bottom. About half of them worked perfectly, but the others need work. I just want a repeatable method and reliable break. The comets were green mix with 25% spherical Ti and a little coarse sponge Ti. The tubes were 9/16" dia. by 2" by 1/8" thick wall. The break was 1/2 tsp hot BP and 1/4 tsp 7/3 with different stars for effect. I could always go with a thinner tube or go up on the burst, but the half of the batch that worked well was really loud and had a nice spread. Does anyone else have any experience with these little guys? I love the simplicity, but they need to work reliably.

Thanks

[Col]

I found the reliability is better with a 4mm clay bulkhead with a passfire hole between the tail comp and the contents. I use 16mm id x 50mm x 0.5mm wall tubes and break them with whistle. They are a versatile effect as you can use them in cakes or canister shells. Depending what you fill them with you get a different effect, eg; stars, crackle or a little flash for timed reports with a tail

 

Heres some that have whistle delay and crackle for the contents, the only difference is they have some empty tube behind the whistle comp to provide the resonating chamber.

 

The tail comp was a bit damp on this one which doubled the delay timing to 4 seconds The insert was filled with 1/8" rolled D1 glitter stars, broken with half a teaspoon of granulated bp and 0.3g of whistle.

http://youtu.be/1sbB8P7_SYk

Edited January 1, 2013 by Col

[Pyrophury]

The problem I was having is that the comet plug was not burning evenly and some of the breaks seemed like it burned through on the edge of the casing or just a pinhole and would just ignite the burst and stars and just spray out the bottom.

 

I'm guessing your rammer has a nipple in the centre to create a passfire hole in the tail/delay comp? Maybe you just need to make this longer, so more of the tail comp remains to provide the necessary containment.