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What's your Holy Grail of Spudguns?

A place to ask general spud cannon related questions.
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Unread postAuthor: MrCrowley » Mon Jan 14, 2008 6:11 pm

Oh and rag for a 500m area, just go on google earth, look at places close to you that are around 500m of empty space, and try and find two landmarks 500m apart.

Like there are some mangroves by my friends house, about 460m wide, 480m from his house. So if I did the same test, according to you, the dart should be imbedded in the bank on the otherside of the mangroves, and that's leaving 20m to physical conditions.

If that dart is brightly coloured and you have a cheap metal detecter, it shouldn't take more then 20minutes to find seraching a 40m^2 area.
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Unread postAuthor: Ragnarok » Mon Jan 14, 2008 7:25 pm

Hotwired wrote:A 16g dart from a 1200mm x 20mm barrel @ 3 degrees with a chamber of say 1000mm x 20mm of 450psi air behind it to go 500m...
...is certainly pushing the boundaries of what I consider likely.

Well, it's a 1200mm by 26mm dia. chamber, but that won't make a vast difference to range.

@MrC: I doubt a metal detector or bright colours will help. I think a dart doing 200 m/s will just hit the ground and be lost below, especially considering there's not much mass of metal there.
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Unread postAuthor: MrCrowley » Mon Jan 14, 2008 7:32 pm

Well you could fire it at a vast amount of concrete 500m away :roll:
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Unread postAuthor: Hotwired » Mon Jan 14, 2008 7:34 pm

Tescos carparks have to be useful for something :wink:
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Unread postAuthor: jackssmirkingrevenge » Mon Jan 14, 2008 11:37 pm

Hotwired wrote:I'm a big fan of practical results so most theories going past me get a pinch of salt.

A 16g dart from a 1200mm x 20mm barrel @ 3 degrees with a chamber of say 1000mm x 20mm of 450psi air behind it to go 500m...

...is certainly pushing the boundaries of what I consider likely.

I'm open to being proved wrong by the ultimate test of a physical demonstration though.


ditto
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Unread postAuthor: SpudBlaster15 » Tue Jan 15, 2008 4:12 am

This thread makes me laugh. Some people just have absolutely no comprehension of precision physics.

Ragnarok has taken the time to write out a fairly lengthy explanation of why he will be able to achieve his goal based on the laws of motion and trigonometry, and it goes completely unread by most of you, and discarded as "theory, not practice" by others.

Take a second to think about what your doubtful theories are based on. Gut feelings. Personally, I would put my trust in thoughtful calculations rather than assumptions pulled out the posterior of one's anatomy.

Aside from that, good luck with your goal Rag. With the massive array of factors your program takes into account, and the fact that it calculates the position of the projectile every 0.1ms, you should very easily be able to calibrate HEAL to hit a target 500m away, assuming you can get an accurate estimate of the projectile's drag coefficient.
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Unread postAuthor: Novacastrian » Tue Jan 15, 2008 5:08 am

I don't doubt Rags math, but i will exploit it! What would be the maximum range of a 1/2" lead sinker with a velocity of 827fps be?
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Unread postAuthor: MrCrowley » Tue Jan 15, 2008 5:58 am

SpudBlaster15 wrote:This thread makes me laugh. Some people just have absolutely no comprehension of precision physics.

Ragnarok has taken the time to write out a fairly lengthy explanation of why he will be able to achieve his goal based on the laws of motion and trigonometry, and it goes completely unread by most of you, and discarded as "theory, not practice" by others.

Take a second to think about what your doubtful theories are based on. Gut feelings. Personally, I would put my trust in thoughtful calculations rather than assumptions pulled out the posterior of one's anatomy.

Aside from that, good luck with your goal Rag. With the massive array of factors your program takes into account, and the fact that it calculates the position of the projectile every 0.1ms, you should very easily be able to calibrate HEAL to hit a target 500m away, assuming you can get an accurate estimate of the projectile's drag coefficient.



I'm sure his math is spot on, but things are different off a chalkboard, there are many cases to prove this. Not everything goes according to a math equation and physics.

There's only one way to find out, so until then...
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 15, 2008 6:09 am

I punched a few numbers into this calculator and got the following data:

Ballistic Coefficient: 0.100 G1 Bullet Weight: 16.00 gm

Muzzle Velocity: 240.0 m/sec

Temperature: 59.00 °F Pressure: 29.92 in Hg
Humidity: 0.0 % Altitude: 0 ft

Std. Atmosphere at Altitude: No Corrected Pressure: Yes
Calculated Parameters
Atmospheric Density: 0.07647 lbs/ft³ Speed of Sound: 340.3 m/sec

Initial Angle: 35.0 deg Terminal Angle: 67.4 deg
Terminal Range: 1088.1 m Terminal Velocity: 65.8 m/sec
Terminal Time: 16.196 s Terminal Energy: 25.6 ft•lbs

It's interesting to note that optimal angles are different for rifled and fin stabilised projectiles, while Rag's calculations are extensive I do not believe they are complete, hence my skepticism.

I don't doubt he can get ranges well in excess of 500 metres with those specifications. but three degress still seems far too low.

you should very easily be able to calibrate HEAL to hit a target 500m away


As to reliably hitting a target smaller than 10 feet square at 500 yards with a subsonic projectile, history has proven this to be highly improbable.
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Unread postAuthor: Hotwired » Tue Jan 15, 2008 1:12 pm

The target I'm making for the shooting clip competiton has started to swell disturbingly in the middle :shock:

Down boy!

*pours cold water over it*


I've yet to get (a) a microphone that works (b) some test clips to see how well this camera captures high speed motion and/or (c) another camera...
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Unread postAuthor: ALIHISGREAT » Tue Jan 15, 2008 1:48 pm

^what is this target and what will you shoot at it?
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Unread postAuthor: Hotwired » Tue Jan 15, 2008 2:24 pm

Not telling :P

It's currently living in a biscuit box and won't be filmed until I'm certain the camera/sound stuff works.

Possibly a metal capped plastic slug. I can mould a polymorph one up in about ten minutes.
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Unread postAuthor: ALIHISGREAT » Tue Jan 15, 2008 2:34 pm

Hotwired wrote:Not telling :P

It's currently living in a biscuit box and won't be filmed until I'm certain the camera/sound stuff works.

Possibly a metal capped plastic slug. I can mould a polymorph one up in about ten minutes.


hmm i'm intrigued, my guess is a phat lump of peanut butter? :D
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Unread postAuthor: Ragnarok » Tue Jan 15, 2008 3:47 pm

@Nova: I make it about 850 yards.

@SB15: Thanks for the vote of confidence.

I'll see if I can put theory into practise, if I can find an area where sending a very pointy 16g lump of steel down range at over 200 m/s won't be dangerous.

@JSR: Ballistic Coefficient and Drag Coefficient are two different things. A low drag coefficient is good, but you want a high ballistic coefficient.
But they are linked by this equation:
Ballistic coefficient = Mass/(Form factor * diameter<sup>2</sup>)
Where form factor is Drag Coefficient of the projectile/ the drag coefficient of the appropriate model.
I'll use the G<sub>1</sub> model, which is it's not the most accurate for this, but there's not a lot in it in the subsonic region, and most bullets are equated on G<sub>1</sub>, so I'll say that to allow comparison.

The value for BC (G<sub>1</sub>) is ~1.66, which is about what I would have expected, and for that it still gives 4.3 km.

My Calculator won't give me more than 3.25 km for that dart and round, so one of them is wrong.
It's one of:
- my calculator is estimating too low, and you already think it's estimation is too high
- The other calculator is wrong, and as it was designed for supersonic rifle bullets, that wouldn't exactly surprise me.
- The G1 model is wildly out for this, and they really don't make a drag model suitable for the dart design, but as I said, in the subsonic region, most models are pretty similar.

However, having looked over this stuff, it gives me lots of ideas on how to handle supersonics in my calculator.
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