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| jimmy101 |
 Posted: 12/05/2008 12:00 PM Post subject: |
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| Ragnarok wrote: | | The interesting part is that the water's surface tension exceeds the forces on it from drag. |
Yep, the terminal velocity is so slow that friction between the air and the surface of the drop is nearly zero. The terminal velocity of a 1.5mm raindrop is only 20~25 FPS (~7m/s). |
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| psycix |
| Posted: 12/06/2008 14:10 PM Post subject: |
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| Ragnarok wrote: | | psycix wrote: | | They are all very amusing, but they dont have much to do with aerodynamic shapes do they? |
Actually, it does. The important point is that water drops in free fall are not the "teardrop shape" they're often assumed to be. |
Which I already posted earlier in this thread. 
| jimmy101 wrote: | | Yep, the terminal velocity is so slow that friction between the air and the surface of the drop is nearly zero. The terminal velocity of a 1.5mm raindrop is only 20~25 FPS (~7m/s). |
Which is probably due to the low sectional density. |
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| jimmy101 |
| Posted: 12/06/2008 16:57 PM Post subject: |
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| psycix wrote: | | jimmy101 wrote: | | Yep, the terminal velocity is so slow that friction between the air and the surface of the drop is nearly zero. The terminal velocity of a 1.5mm raindrop is only 20~25 FPS (~7m/s). |
Which is probably due to the low sectional density. |
Yep, with a density of just 1g/cc water makes a pretty crap "shell". Lead is 11.3g/cc. 11.3 times as much mass, 11.3x the sectional density for a sphere, basically the same Cd. Water would make a pretty crappy bullet. |
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| Ragnarok |
| Posted: 12/06/2008 17:50 PM Post subject: |
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| jimmy101 wrote: | | Water would make a pretty crappy bullet. |
It would... but that does bring up the question of ice bullets. Clearly ballistically and terminally poor with a density of even less than water, but very hard to trace forensically, as they would quickly melt away.
I know the Mythbusters got bad results with making and firing them, but that is in a rifle with very high pressure, high temperature gases - but what about in a reasonably high pressure, low-ish calibre pneumatic spudgun?
Obviously, I'm not suggesting the use of it, but it is an interesting question.
I reckon that with a decent mould, you could make a hollow tailed projectile that would exhibit good stability and passable accuracy - and you could make up for the low density by making a fairly long projectile to improve the sectional density.
Might be interesting to look into. |
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| jackssmirkingrevenge |
| Posted: 12/06/2008 18:34 PM Post subject: |
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| Ragnarok wrote: | | I reckon that with a decent mould, you could make a hollow tailed projectile that would exhibit good stability and passable accuracy - and you could make up for the low density by making a fairly long projectile to improve the sectional density. |
The hollow tail would probably shatter on firing. I think that - speaking theoretically, of course - you'd have to be at a few yards range anyway, close enough for stability not to matter. There's definitely no question of having any significant accuracy beyond a target that's in the same room. |
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| Ragnarok |
| Posted: 12/06/2008 19:42 PM Post subject: |
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| jackssmirkingrevenge wrote: | | The hollow tail would probably shatter on firing. |
Depends on how hollow. I think that if the outer diameter matched the diameter of the pipe it was being fired from closely enough, the gases in the tail would force it against the walls not unlike an airgun pellet's skirt does
With something like my porting muzzle attachment, you could then kill the barrel pressure at the muzzle end very quickly so that once the support of the walls was lost, there was no pressure on the inside either.
I'll add it to my list of "Things to try sometime", see what kind of results I can get at range. Obviously in practical terms, an untraceable ice bullet is no use unless you're at least far enough from your target that you can't be identified yourself. |
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| inonickname |
| Posted: 12/07/2008 18:29 PM Post subject: |
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| jimmy101 |
| Posted: 12/07/2008 19:56 PM Post subject: |
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I don't think it would be difficult to get an ice slug up to lethal KE's with sufficient accuracy at say a 100 foot range.
Heck a basic cylinder from a rifled barrel, or even a sphere from a rifled barrel should do the trick. Perhaps not the most elegantor efficient round but certainly should be possible to get enough accuracy and KE to do "significant damage". |
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| Ragnarok |
| Posted: 12/07/2008 20:18 PM Post subject: |
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Lord of Karma
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| jimmy101 wrote: | | I don't think it would be difficult to get an ice slug up to lethal KE's with sufficient accuracy at say a 100 foot range. |
Yeah, but 100 feet is still close enough that it's kind of pointless trying to hide the ballistics or evidence by using an ice bullet - you're close enough to be traced, unless of course you have a compact and near silent launcher which can generate a reasonable KE, and that's no mean feat.
I was thinking out beyond at least 100 yards myself, far enough that you're far enough away that it will be starting to get hard to spot or identify where you shot from. |
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| psycix |
| Posted: 12/08/2008 10:02 AM Post subject: |
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Or let the slugs rain down from the sky by firing them upwards like long range artillery.
Could fire it over a few houses, so you are not in the line of sight. |
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| jimmy101 |
| Posted: 12/08/2008 11:18 AM Post subject: |
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| Ragnarok wrote: |
Yeah, but 100 feet is still close enough that it's kind of pointless trying to hide the ballistics or evidence by using an ice bullet - you're close enough to be traced, unless of course you have a compact and near silent launcher which can generate a reasonable KE, and that's no mean feat. |
Kennedy was shot from a range of about 180 feet. People in the area could not localize the shooter. 40+ years later it still can not be proven where the shooter(s) was(were) based on the audio recordings of the event.
100' is probably far enough. As long as there is no one close to the muzzle and it is a complex accoustic location (i.e., around buildings).
The human ability to localize a sound is really pretty poor. Especially when the sound was unexpected and there is an echo. People are so bad at it that the military uses accoustic devices to localize enemy shooters. |
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| Lentamentalisk |
| Posted: 12/08/2008 15:34 PM Post subject: |
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| jimmy101 wrote: | | The human ability to localize a sound is really pretty poor. Especially when the sound was unexpected and there is an echo. People are so bad at it that the military uses accoustic devices to localize enemy shooters. |
It should be noted that mainly these are used on Humvees, because they are too loud inside to have the slightest clue where shots are coming from. |
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| Floyd |
| Posted: 12/16/2008 14:57 PM Post subject: |
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| Whoa, I haven't checked this thread for a while until I saw it on this wiki page. I thought why would that be on the wiki page and then I looked here and saw all of the replies. Thanks a lot for the discussion, I learned a lot from reading it. I am going to do the fair, but I don't plan on going any higher than the school level. |
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| Ragnarok |
| Posted: 12/16/2008 15:14 PM Post subject: |
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Lord of Karma
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| Floyd wrote: | | I thought why would that be on the wiki page and then I looked here and saw all of the replies. |
It would be on the Wiki Page because I thought it contained some good information. |
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| raptorforce |
| Posted: 12/16/2008 22:46 PM Post subject: |
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| wow not fun reading 6 pages of comments to catach up i ve made some projectiles like its a spitzer design with a steel tip but is surrounded by wood. i am going to try fill it with lead solder and put a steel tip on top of that as i cannot find any harder material that i can get but i do have my eye carbide for some reason i cant upload a picture |
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