# Why is 50% of a bombs weight in the casing?
**URL:** https://boards.straightdope.com/t/why-is-50-of-a-bombs-weight-in-the-casing/271331
**Category:** Factual Questions
**Created:** [October 26, 2004, 11:33pm UTC](https://boards.straightdope.com/t/why-is-50-of-a-bombs-weight-in-the-casing/271331 "2004-10-26T23:33:43Z")
**Posts on this page:** 7
**Page:** 2
### Author:  [@Loach](https://boards.straightdope.com/u/Loach)
#### Post date: [October 28, 2004, 1:56am UTC](https://boards.straightdope.com/t/why-is-50-of-a-bombs-weight-in-the-casing/271331/21 "2004-10-28T01:56:01Z")
> [@](#):
>
> Another advantage is that these casings burn up on firing, saving you from getting stacked knee-deep in empties.
Like you said :smack:
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### Author:  [@Boyo\_Jim](https://boards.straightdope.com/u/Boyo_Jim)
#### Post date: [October 28, 2004, 2:10am UTC](https://boards.straightdope.com/t/why-is-50-of-a-bombs-weight-in-the-casing/271331/22 "2004-10-28T02:10:51Z")
> [@Loach](#):
>
> If it is made out of the same substance that 120mm sabot and HEAT rounds are made of then it would be plenty durable to be strapped to the outside of a jet. I don’t know what would happen on impact.
>
> In case you are wondering, the cellulose casing of a 120mm round burns up when it is fired leaving only the aft-cap (the metal plate on the bottom containing the primer). It makes the inside of the turret a lot less messy after firing a few rounds. The 105mm gun in the old M1 leaves behind a two foot metal casing.
You may be right but I’m not following the logic here.
You say this cellulose shell casing is used in M1 tanks. So it’s carried around and never subjected to more than 3 or 4 g’s when the tank is maneuvering. And it’s almost certainly not subjected to anything like the temperature and humidity variations it would find on a plane. And when the shell _is_ fired, the casing burns off in microseconds from a single ignition source.
And this gives you confidence that it would make reasonable strap on weapon to a supersonic jet? Except for your issue with impact, of course. 😕
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### Author:  [@Danalan](https://boards.straightdope.com/u/Danalan)
#### Post date: [October 28, 2004, 2:13am UTC](https://boards.straightdope.com/t/why-is-50-of-a-bombs-weight-in-the-casing/271331/23 "2004-10-28T02:13:24Z")
[Here](http://www.smh.com.au/articles/2003/04/06/1049567567365.html?oneclick=true) is a bomb with no explosives – urban combat requires interesting technology. Yep - laser guided concrete.
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### Author:  [@Boyo\_Jim](https://boards.straightdope.com/u/Boyo_Jim)
#### Post date: [October 28, 2004, 2:32am UTC](https://boards.straightdope.com/t/why-is-50-of-a-bombs-weight-in-the-casing/271331/24 "2004-10-28T02:32:26Z")
> [@Danalan](#):
>
> [Here](http://www.smh.com.au/articles/2003/04/06/1049567567365.html?oneclick=true) is a bomb with no explosives – urban combat requires interesting technology. Yep - laser guided concrete.
Your site requires a registration.
[Here is a BBC link that doesn’t.](http://news.bbc.co.uk/2/hi/middle_east/2919249.stm)
I have to say I think this is a great idea. It might be a spinoff of some star wars concepts that imvolved placing objects in orbit that could be “dropped” onto ground targets and kill with kinetic energy.
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### Author:  [@Loach](https://boards.straightdope.com/u/Loach)
#### Post date: [October 28, 2004, 2:50am UTC](https://boards.straightdope.com/t/why-is-50-of-a-bombs-weight-in-the-casing/271331/25 "2004-10-28T02:50:15Z")
> [@](#):
>
> And this gives you confidence that it would make reasonable strap on weapon to a supersonic jet?
I have no scientific evidence, just my perception from handling many rounds. If you held one you would think it is made out of some sort of metal or hard plastic. I’m not sure what you think g-forces would do to a bomb. The laser seeker in bombheads are made out of glass and plastic. They hold up pretty well under g-forces. What do you expect heat and humidity to do? The highest temperature would be somewhere around 115f, the same temp that it will reach in a tank in the desert. The lowest temperature would be what? Much lower than a bad winter in Germany or Korea? The casings are coated and water proof. So yes I don’t know what an impact from 20,000 feet might do but I’m pretty confident that it would be able to stand up to whatever an old dumb bomb, a laser smart bomb, an external fuel tank or an electronics warfare package can handle. Don’t think of cellulose as paper, it actually acts more like a ceramic until expose to high heat in the gun barrel.
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### Author:  [@mks57](https://boards.straightdope.com/u/mks57)
#### Post date: [October 28, 2004, 4:11am UTC](https://boards.straightdope.com/t/why-is-50-of-a-bombs-weight-in-the-casing/271331/26 "2004-10-28T04:11:35Z")
As previously mentioned by Roches, safety would be a major concern with a cellulose casing.
There is an excellent documentary named “Situation Critical” on the fire that occurred on board the carrier USS Forrestal in 1967. It is occasionally shown on the Discovery Channel. John McCain, future POW and Senator, was sitting in his aircraft on the flight deck when it was hit by an accidentally fired Zuni rocket. He escaped the aircraft but the fire rapidly spread across the flight deck. It includes footage of fire crews attempting to extinguish multiple fires on the flight deck while GP bombs and other ordnance are cooking off.
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### Author:  [@Princhester](https://boards.straightdope.com/u/Princhester)
#### Post date: [October 28, 2004, 8:48am UTC](https://boards.straightdope.com/t/why-is-50-of-a-bombs-weight-in-the-casing/271331/27 "2004-10-28T08:48:57Z")
> [@Airman Doors](#):
>
> The book is way, way, way better than the movie. Actually, I can’t think of a case where this isn’t so.
Star Wars. 🙂 Sorry. Carry on.
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