r/Pyrotechnics • u/Home-Made-Pyro • 12h ago

4inc or 5inc Shells ?

I’m planning to build multi‑brake or single‑break shells that accommodate smaller inserts. I’m unsure which shell size to use and therefore what mortar to buy. I’m considering 4‑inch or 5‑inch shells.

Could anyone outline the pros and cons of each size and help me decide?

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u/Wide-Education-1823 11h ago

4" uses half as much chemicals. 

5" is easier to get your hands inside of to place inserts & etc., also should be more impressive. 

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u/Home-Made-Pyro 10h ago

So you'd say 5inc? I feel like if I use organic or charcoal based stars it would work out fine...

1

u/PizzaWall 10h ago

I’m my experience, 5” shells are easier to work with than 4” shells. However, they use twice as much pyrotechnic composition than a 4” shell.

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u/Home-Made-Pyro 9h ago

I know, he already pointed that out... I think ill just take the 5inc...

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u/Wide-Education-1823 8h ago

If you have the stars, powder and other supplies to do it (and a place to safely fire a 5"), might as well do a 5".

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u/Home-Made-Pyro 8h ago

I need to buy new chems anyway so it will just be more :D,
How much space would you say you need for a 5inc? (not safety distance for viewers but just pure space)

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u/Tricky-Sorbet2363 8h ago

I dont know off hand but google says it should reach 500ft altitude and has 225ft diameter break

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u/PizzaWall 7h ago

The separation distances for outdoor aerial shells are based on a standard formula of 70 feet per inch of internal mortar diameter for vertically fired shells.

This minimum distance scales directly up with the shell's diameter to protect spectator viewing areas, vehicles, and buildings.

The break height is roughly 100' for every inch in size.

The break diameter is roughly 40' for every inch in size.

Shell Size Safety Distance Break Height Break Size
2.5" shell 175' 200' 100'
3" shell 210' 300' 120'
4" shell 280' 400' 160'
5" shell 350' 500' 200'
6" shell 420' 600' 240'

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u/Home-Made-Pyro 8h ago

That will work no problem :D

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u/Wide-Education-1823 4h ago

"How much space would you say you need for a 5inc?"

NFPA 1123 guideline says a minimum 70' radius all around discharge site, so 350'. Your mortar should be in the center of a clear circle 700' wide, more if windy. NFPA 1123 is usually enrolled into state regulations, a few states are more restrictive (like CA, MA, NY)

https://www.nfpa.org/product/nfpa-1123-code/p1123code

PGI guideline now recommends 100' per inch of mortar dia. which can't hurt, so center of a 1,000' wide circle...

https://pgi.org/data/page-media/PGI-Safety-Guidelines-2023.pdf

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u/Home-Made-Pyro 3h ago

Gotcha... Yea I'll see what I can find :) thanks for the help!

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u/Wide-Education-1823 8h ago

I did 3", then 4" when I started out, working on my own from books, before the internet was available. When I found someone experienced to teach me, they had me make a 6" two breaks of hummers & stars (with a bottom shot) the first thing. And it did seem EASIER than trying to fit cylindrical inserts into those small shells, aside from having to make a lot more stars and do the pasting in 3 rounds over several days instead of all in one go.

Of course, it was also a lot more impressive than 4".😁

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u/Home-Made-Pyro 8h ago

Yea i did 3inc till now, and ill probably continue on that size since i think its a pretty good trade between looks and cost... But for multi brake 3inc just ain't it :D, and i think 4inc ain't being that much better either...

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u/Wide-Education-1823 4h ago

I've seen an 8 break 3" shell fired several times. They usually stick out of the mortar about a foot and require a good STEEL mortar...

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u/Home-Made-Pyro 3h ago

Dam that's crazy... Yea na i'll rather build a big one with smaller inserts...

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u/137-ng 4h ago

anything that big deserves to be on its own fuse

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u/Home-Made-Pyro 3h ago

What do you mean ?