Figuring Burst charge

[BJV]

You have Rice Hull weight x. Cotton seeds weight x

and Cork weight x. How do you figure the ratio. Say 1 to 1

by weight or volume?

BJV

[Mia]

BJ I use a 1/1 mix with a good fast powder; I have used the Toro method before works great.

Oh that’s by weight sorry

Edited May 17, 2013 by Mia

[Bcorso85]

I Measure by weight. But when I think about it I don't think I've ever read it specified.

[FlaMtnBkr]

I'm not sure I know exactly what you are asking but I think you are asking about substituting one medium for another? I have only used rice hulls and don't know how the density of the other mediums compare. But if you are using say 6:1 BP to hulls, then I would think you have a certain weight of BP per volume of coated hulls. I don't think the weight is important but that ratio is what most people use with good results. If replacing the media, I would be inclined to do so by volume. I would think that way you would stay close to the same density of coated burst. Again, I haven't tried so I don't know for certain but it seems right.

 

If you are asking how much BP goes on the hulls then I have read anywhere from 4:1 to 7:1, with 6:1 probably the most common and what I use. That is black powder to dry hull weight. I'm sure when dialing in burst this needs to be looked at as well as BP strength, layers of paste and paper (or tape) for a round shell and spiking for a cylinder shell (and probably other variables that I don't know about as I don't make them), and the use of a booster such as flash. Plus probably humidity, moon phase, and how you hold your mouth during assembly. There is also quite a bit of experimenting to get things working as good as possible, at least in my experience and I'm sure I still have a long ways to go. Hopefully I have explained things well enough that you can follow what I'm trying to say.

[pyrojig]

Most everything in that regard is by weight unless specified. As per amount of powder coating per ea. type of medium, that will vary a lot. Most common is the rice hulls and seed that the Chinese use for burst. Im sure there will be less burst powder on cotton seed( being more dense) than rice hulls, if the same weight ratios are used. It is a common statement, and a loose rule to follow. One must do some testing to get the preferred results from their burst. It is more critical to obtain less powder in a pattern shell, or a large caliber shell( to not over break them). Also not to mention that fire transfer is much diff in the large burst medium. Large medium is preferred to the rice hulls which can block fire transfer to the stars on both sides of the hemi .

 

*Where the burst coating is most critical is with H3 or KP. This is where the excessive coating will reduce the power( not all is consumed before the shell breaks), as well as lack of consistent sizing of the medium to be coated.

 

FlaMtnBkr had a good point as stated above, many factors go into the equation of balancing your burst to get it to do what you want.

[burningRNX]

I think you have to experiment and try batches to dial in a specific weight BP per volume burstcharge.

 

Weight a given volume of burst, say MCRH 4:1, divide the outcome by 5 (4+1) and calculate the weight of BP in that volume.

Do that with another burst carryer and compare the results, if the amount of BP is lower, coat more untill it has the same amount of BP on it

Edited May 18, 2013 by burningRNX

[Xtreme Pyro]

I measure by weight as well. For example if I wanted 5:1 BP to Hulls, I'd have 5 pounds of powder to one pound of hulls.

[FlaMtnBkr]

I'm pretty sure he is asking about switching between rice hulls, cotton seed, and cork. And do you exchange one for another by weight or volume. I still think a substitution by volume would give the most similar burn characteristics to the original burst if coating with the same type and weight of BP.

 

Maybe he will clarify what he was asking. If I had some cotton seed I would go out and experiment. Maybe I will try some puffed rice cereal instead as that is available locally.

[BJV]

Thanks for everyone's input. Here is what I found in Shimizu's book (FAST)

BJV

[marks265]

Your ratio will vary as "your milage may vary". When increasing or decreasing the ratio you are fine tuning the strength of your burst. The carrier used sets a grain size. Usually the smaller grained media is used for smaller shells and of course bigger grains for bigger shells. When the burst charge cannot be made strong enough when fine tuning with a selected carrier a smaller carrier can be tried. However, I think most people just skip right to slow flash or some other booster. Just another lovely example of us pyros workin' with what we have

 

Mark

[FlaMtnBkr]

Strange that he doesn't specify the cork size since it can come in all different sizes. And is cotton seed bigger or smaller than rice hulls? I would think smaller? I also need to dig out my copy of FAST and see what # 5, 44, and 46 are. I assume they are hotter than BP.

 

In smaller shells I don't use coated media and just use larger mesh polverone. For small shells, instead of using a booster like flash, the BP can be coated in dark aluminum to make the break harder and give them more 'noise'. In some small Chinese bombettes there is no BP used at all, just flash. I would assume a slow KNO3 based flash though and small rock hard stars would be required. In fact fine tuning the stars to survive the break and remain lit at high speed is probably the hardest part.

[Mumbles]

Cotton seeds are much larger than rice hulls. Probably about a quarter inch wide and half an inch long in most cases. They're also a solid quarter inch thick too. I don't know how the volume compares, but they're certainly much heavier than rice hulls.

[BJV]

Here is a photo of cotton seed and rice hulls side by side.

10 grams each

BJV