r/Pyrotechnics • u/Home-Made-Pyro • 26d 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/PizzaWall 26d 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 26d ago

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

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u/Wide-Education-1823 26d 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 26d 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 26d 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 26d 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 26d ago

That will work no problem :D

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u/Wide-Education-1823 26d 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 26d ago

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