Shimizu: Amount of burst charge

[AdmiralDonSnider]

Today I assembled my first 3" sphere (Warimono) and reviewed a table in FAST p. 252. While I closely corresponded to the star size, using chlorate stars of 9mm diameter when primed, I´m quite sure the H3 coated hulls I loaded (4:1 ratio) come nowhere near the 35g (without cores) given by Shimizu. I properly loaded the shell, filling up the tissue-lined center, slightly overloading to make sure the contents are locked in position as suggested.

 

35g plus core (hulls) of H3 coated hulls take up a lot of volume and I´m not sure how someone manages to get them all loaded... just curious if his specs are correct or if I made a mistake.

 

Does he even speak of H3? Would BP on hulls weigh that much more?

Edited February 11, 2010 by AdmiralDonSnider

[AdmiralDonSnider]

No ideas, anyone?

 

The guys on rec.pyro didn´t know an explanation either...

[50AE]

I can't help you much, but I don't think H3 and BP have a big difference in weight.

And 35g of H3 on hulls seems too much for a 3" shell. I doubt you can put that much. Maybe 35g of H3 in granulated form instead.

Why do you want to be precise in the burst quantity anyway? I always fill my 3" shells with as much burst charge they can carry. I never measure the mass of the stuff I put inside and I get good breaks.

Edited March 8, 2010 by 50AE

[Pretty green flame]

There's no need to make pyrotechnics into an exact science. Use BP on rice hulls (or another substrate) then find out (by testing ofcourse) how much flash booster you need for a decent break. As far as i'm concerned flash is the only composition that you have to measure how much to put in a shell. In small shells atleast I consider flash to be the "main" burst charge, BP on hulls is just a flammable filler, flas is what makes your shells burst nice and big (unless you want to go over the top with pasting your balls). So I wouldn't bother too much with such exact numbers.

[xetap]

35g plus core (hulls) of H3 coated hulls take up a lot of volume and I´m not sure how someone manages to get them all loaded... just curious if his specs are correct or if I made a mistake.

Smaller hulls or a higher ratio (like 6-7:1) is about all I can see and even that doesn't make THAT much difference.

 

What would 35g of 4:1 look like, just poured into empty hemi's?

[AdmiralDonSnider]

There's no need to make pyrotechnics into an exact science. (...) So I wouldn't bother too much with such exact numbers.

 

I was just curious and wanted to grasp the table. Scientists like Shimizu usually don´t create useless tables. Why not use his values as a starting point, his specs for star size did work very well...

 

Smaller hulls or a higher ratio (like 6-7:1) is about all I can see and even that doesn't make THAT much difference.

 

What would 35g of 4:1 look like, just poured into empty hemi's?

 

Nope, it doesn´t. Even BP on hulls or granulated H3 wouldn´t reach the 35g.

I guess this weight could at least fill two complete sets, with stars removed.

[Mumbles]

I did a quick calculation. I figured around 2 3/8" for the burst area(probably big, but the rice will compress too), which is only about 36mL, and rice hulls run around 7-8 mL per gram. 4:1 is around 22g, and 7:1 is around 40g. This of course doesn't take into consideration any size growth from coating the burst on, which I am sure is substantial. I believe the rice hulls of Shimizu's experimentation are different from the shredded wine making product we have. It could be denser or have different loading properties. I also don't measure my burst by mass, but just use standardized ratios and make things work for me. I use KP-like mixes, so things are a little different.

[PoorBoy]

i was actually looking for this topic to answer questions of my own. and i found some info that may or may not be relevant. to get to the 35g sky lighter suggests using redgum granulated BP instaed of coated on ricehulls in smaller shells. I was reading the tut. on making 4" zinc shells and in the 4" shells they use granulated bp. That seems like a waste to me because thats like a half pound. I was looking around because bp on rice hulls alone wasnt breaking my shells hard enough, they looked pretty and all but i can usually find the un broken hemis on the property. i think im gonna give up on shimzus table and use some mid grade flash for a harder break. Skylighter had a table which had the different weights per inch of rice hull BP and granulated and ETC. granulated seems a little pricey for me though.

[dagabu]

Poor boy, try 6-8 grams of whistle mixed with the coated rice hulls.

 

D

[PoorBoy]

Poor boy, try 6-8 grams of whistle mixed with the coated rice hulls.

 

D

 

 

thanks, i just looked across the forum and realized i dont have the benzoates or salicylate to make whistle so im limited to slow flash for now. if u were using bright flake, how many grams of slow flash would u put in a 4" shell?

[qwezxc12]

thanks, i just looked across the forum and realized i dont have the benzoates or salicylate to make whistle so im limited to slow flash for now. if u were using bright flake, how many grams of slow flash would u put in a 4" shell?

 

 

I typically use a 70:30 slow flash made with -325m bright flake for booster in my shells. Burst is 4:1 Alder BP on rice crispies or hulls. Booster is loose and lightly worked into the burst media, half in each hemi:

 

5g in a 4in

20g in a 6in

 

Plastic hemi's are pasted with three 50% overlapping (six layers) of 60lb. re-enforced gummed tape. Each layer rotated 90º so the poles don't build up. They break big and loud.... YMMV.

Edited April 2, 2010 by qwezxc12

[PoorBoy]

thanks thats great, i'm gonna do that and see how it works for me. !!!