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Amount of comp needed to make X number f stars?


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#1 warthog

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Posted 05 May 2012 - 03:44 PM

First and foremost, I do realize that the densities of various formulae differ so that 100 grams of one will make X number of stars of a given diameter while the same 100 grams of a different composition may yield more or less stars than the former. However there must be some average weight that one can use to calculate how many stars can be made in order to avoid having way too many or too few to make the desired number of shells. The overall goal is to avoid havig a lot of excess stars after the shells you want to make are done. This is what I am wondering if anyone has ever figured out. If not, perhaps in your experience you may have decided upon a number that has worked out well for you when this sort of thing is your goal.

For example, if I wanted to make a single 6" ball shell, say this will take approximately 440, 1/2" square* pumped stars to fill. How much comp in general would you make to get this done with a minimum of overages?

Anyone ever decided upon a number for themselves, used it and found it works?

Thanks! :)


*a square pumped star is as long as the diameter of the pump.

Edited by warthog, 05 May 2012 - 03:45 PM.

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#2 Potassiumchlorate

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Posted 05 May 2012 - 03:50 PM

Well, it will be about 100 stars, not 440. ;)

I think 600 or 700 grams of composition if they are barium chlorate or strontium nitrate stars.
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#3 warthog

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Posted 05 May 2012 - 04:57 PM

a SIX INCH shell with Half Inch pumped stars? 100?

You guys must have smaller inches over there than we do...

I guess I will have to count them as I place them this time. :)

Edited by warthog, 05 May 2012 - 04:58 PM.

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#4 MikeB

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Posted 05 May 2012 - 07:19 PM

Off the top of my head, so this will be close but not accurate. A lot depends on the comp, pressure, cut, rolled, or pumped.
pumped stars: 3/8 inch = 1 gram
1/2 inch = 2.5 grams
3/4 icnh = 9 grams

Cut stars: 100 half inch stars to the pound

Rolled stars are about 2/3 the volume and weight of pumped stars

Just make twenty or forty pound batches of stars. That way you won't run out.

Edited by MikeB, 05 May 2012 - 07:21 PM.

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#5 warthog

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Posted 06 May 2012 - 02:58 AM

Thanks Mike, that helps.

Maybe I will just make 30-40 pounds... :)
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#6 pdfbq

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Posted 06 May 2012 - 05:31 AM

I think with some relatively simple math you'll be able to calculate the amount of stars :)

First surface of a sphere:
For pumped stars you need the *inner* sphere you will create when putting in the pumped stars.

Say the inner diameter of your 6" hemi is 5,25 inches and your pumped stars are 1/2 inch.
Your *inner* sphere diameter is: 5,25 - (2 * 1/2) = 4,25

The formula for the surface of a sphere is 4πr2 so:
4 * π * (4,25/2)2 = 86,6 which would mean ~346 square 1/2" stars (optimum).
This will tell you that the factor for nice circle packing is ~ 0.907 so:
346 * 0.907 =~ 314 pumped 'round-square' 1/2" stars.

Volume cylinder: πr2*h so one (1) of your pumped stars has a volume of π(1/4)2*(1/2) =~ 0,09822 inch.
So total volume of the stars: 314 * 0.0982 =~ 30,82 inch.

Only thing you have to know now is the density of your comp in these stars. I you have some left overs weigh them, or do a dry pump etc..

Edit: The math needed for a 100% accurate calculation is much more complex but does not make a better prediction.

Edited by pdfbq, 06 May 2012 - 05:59 AM.


#7 Potassiumchlorate

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Posted 06 May 2012 - 06:33 AM

Hm, sorry, I miscalculated. I was thinking about 20mm stars. :blush:
"This salt, formerly called hyperoxymuriate of potassa, is used for sundry preparations, and especially for experimental fire-works." Dr. James Cutbush

Conflo, ergo sum

#8 warthog

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Posted 06 May 2012 - 07:12 AM

Thanks pdfbq, my math was wrong as I used a calculator on Passfire to do the math for me and I did some rounding I should not have or it would have been closer. My problem was I was quite sure it would take more then 100 stars which is clear by your calculation. I also see there was a bit of a mix-up due to the english units vs the metric an I was sure this was where KCLO3 had gone wrong as well.

I knew my number was high, I called it a 6" shell when I also know the ID is less than 6". Thank you for a more precise number.

Edited by warthog, 06 May 2012 - 07:12 AM.

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#9 bob

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Posted 06 May 2012 - 01:48 PM

I don't make stars for a giving shell I just make about 1000 stars at a time and then I don't have to make stars for a while
if you really can't have leftovers just make some simple mines
just a thought
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#10 Potassiumchlorate

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Posted 07 May 2012 - 05:29 AM

When I fill a 6" with magnesium fueled stars, I make the stars large, 20mm. For barium chlorate stars it seems like 10mm would be more suitable. The 20mm burn too slowly, at least the "classic" 9:1 barium chlorate/shellac composition.

Edited by Potassiumchlorate, 07 May 2012 - 05:29 AM.

"This salt, formerly called hyperoxymuriate of potassa, is used for sundry preparations, and especially for experimental fire-works." Dr. James Cutbush

Conflo, ergo sum

#11 Mumbles

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Posted 07 May 2012 - 09:49 AM

When using such large stars, you run the risk of the breaks starting to look sparse or having substantial droop on the stars. There is a particular type of shell that utilizes very bright and often large stars (a dahlia), but that isn't for everyone of course.
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#12 Potassiumchlorate

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Posted 07 May 2012 - 10:28 AM

When using such large stars, you run the risk of the breaks starting to look sparse or having substantial droop on the stars. There is a particular type of shell that utilizes very bright and often large stars (a dahlia), but that isn't for everyone of course.


I know. I put 20mm barium chlorate stars in two 6" for New Years Eve, and they were beautiful in colour but drooped quite a bit, some even reached the ground. :blush:

All my big magnesium stars burn perfectly OK, though. B)
"This salt, formerly called hyperoxymuriate of potassa, is used for sundry preparations, and especially for experimental fire-works." Dr. James Cutbush

Conflo, ergo sum

#13 warthog

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Posted 07 May 2012 - 01:03 PM

What size pumped star is best to use in a 6" ball shell?

Bob, that has been what I have been doing. It is a waste of money and time to be making mines all the time when that wasn't what I had wanted to do. I suppose I don't like to store a lot of excess product and that is my particular way of doing it. I try to make it all as efficient as I am able. I do make some things in batches so I don't have to make them all the time, like coated rice hulls and BP for lift.

As I have said, I am still quite new. With this comes a fair bit of experimentation to see what sorts of color comps and other effects I personally prefer to use in my own shells and other items. This is why I don't want nor need a lot of excess stars laying around, what if they aren't what I like? Make a mine or burn them? I still paid for the chemicals and spent the time to make the extras, right? IMO that just feels wrong so until I get to a place where I have some good, basic stars I want to use all the time (Not to say I won't always be looking to improve mind you)), I only want to make what I plan on using up. No doubt about it though, when I get myself situated, I will certainly be making several pounds of each type of star I like so I have them when I ned them. I hope this helps you to understand why I asked in the first place. :)

Edited by warthog, 07 May 2012 - 01:05 PM.

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#14 dagabu

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Posted 07 May 2012 - 01:06 PM

What size pumped star is best to use in a 6" ball shell?


I shot a 6" ball shell with 1/2" pumped stars this weekend and the spread was just a little large and sparse for my likes, 3/8" would have been perfect.

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#15 Potassiumchlorate

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Posted 07 May 2012 - 01:36 PM

Hm, my chlorate stars, except for the barium chlorate stars, are usually 15-16mm, i.e. about 5/8". I think they burn very fast, Bleser Aqua for example. I see that you guys often use perchlorate stars, though.
"This salt, formerly called hyperoxymuriate of potassa, is used for sundry preparations, and especially for experimental fire-works." Dr. James Cutbush

Conflo, ergo sum

#16 warthog

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Posted 07 May 2012 - 02:07 PM

Thanks Dag, looks like my little chart os off a bit then.

I guess when I am able to do more real life experiments, it will be a lit easier for me. :)
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If you confess with your mouth, "Jesus is Lord" and believe in your heart that God raised Him from the dead you will be saved. For it is with your heart that you believe and are justified, and it is with your mouth that you confess and are saved. (Romans 10:9-10).

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