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spudgun range, are we falling short?

A place to ask general spud cannon related questions.
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Unread postAuthor: jackssmirkingrevenge » Wed Mar 30, 2011 3:11 am

Ack, missed it. Cheating? Let me guess...
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Unread postAuthor: Labtecpower » Wed Mar 30, 2011 3:19 am

Your guess is right...

Should I post my diagram? :)
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Unread postAuthor: jackssmirkingrevenge » Wed Mar 30, 2011 3:27 am

As Tech pointed out, it would be against forum rules *cough*PM*cough* ;)

There are non-pyrotechnic ways of "cheating" too, but it is out of the scope of what this thread was attempting to achieve.
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Unread postAuthor: ilovefire » Wed Mar 30, 2011 3:51 am

what about a fin stabilized co2 capsule with a sabot that has a puncturing tip in it to make a small hole in the back? so then it would be kinda like a mini gas rocket, not against the rules is it
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why make it if it dosent shoot?
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Unread postAuthor: jackssmirkingrevenge » Wed Mar 30, 2011 4:02 am

ilovefire wrote:so then it would be kinda like a mini gas rocket


... as well as providing a "base bleed" effect, the thrust isn't inconsiderable either:

[youtube]http://www.youtube.com/watch?v=FO2wA2x_5Q8[/youtube]

Do they teach grammar in colledge :roll:
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Unread postAuthor: ilovefire » Wed Mar 30, 2011 4:14 am

yes i have seen those done before and ever since then i have wanted to see how well it would go with just the capsule and not the car, would be even better if it had another kind of acceleration like being shot out of a cannon
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Unread postAuthor: jackssmirkingrevenge » Wed Mar 30, 2011 5:16 am

There have been several suggestions both on this forum and on spudtech for a launcher that was basically a tube with a firing pin that would rupture the seal on a CO<sub>2</sub> capsule, however I don't think this would be as effective in terms of range and velocity as having the capsule launched from a conventional high performance launcher, then having the seal ruptured at some point after it has left the muzzle.

Has anyone ever shot a water rocket out of a spudgun?
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Unread postAuthor: ilovefire » Wed Mar 30, 2011 5:18 am

jackssmirkingrevenge wrote:Has anyone ever shot a water rocket out of a spudgun?


how would that work? like setting it of?
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Unread postAuthor: Labtecpower » Wed Mar 30, 2011 5:23 am

I made a water-rocket bazooka when I was 8 or so..

Maybe it is a fun project to do again. The weather is getting warmer, getting wet shouldn't be a very big problem.


I also sold a water rocket pistol to a teacher.
Here's a picture:

Image
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Unread postAuthor: MrCrowley » Wed Mar 30, 2011 5:57 am

@JSR,

With the Sears-Haack bodies, do they need to be spinning? Might just stick to conventional finned projectiles if so since they're probably easier to construct.
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Unread postAuthor: LeMaudit » Wed Mar 30, 2011 6:17 am

jackssmirkingrevenge wrote:They look vaguely like the shells fired by the Anzio Annie :D


Not "vaguely" :D And you know your guns! ;-)
BTW I think the article is wrong. The barrel was riffled, and the splines engaged into it.

jackssmirkingrevenge wrote:Some good discussion of cast projectiles here.


Quite an interesting read to wake up slowly and start the brain, thanks for all the links!
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Unread postAuthor: jackssmirkingrevenge » Wed Mar 30, 2011 7:53 am

ilovefire wrote:how would that work? like setting it of?


Pressurised water rocket loaded into spudgun, rocket nozzle activated by a chord or similar device tied to the launcher which opens the flow once the rocket is clear of the muzzle.

Labtecpower wrote:I also sold a water rocket pistol to a teacher.


Looks good, is the trigger a quick-connect?

MrCrowley wrote:With the Sears-Haack bodies, do they need to be spinning? Might just stick to conventional finned projectiles if so since they're probably easier to construct.


A Sears-Haack body is too long to be gyroscopically stabilised - going by the Greenhill Formula, a 0.25" diameter 2.5" long lead projectile would need a twist rate of 1 turn every 3.75 inches (by contrast typical 22LR twist rate for example is 1 in 16) - however I'm not sure if it can be stabilised by forward CG alone. Personally if fins could be avoided I think it would be better.

And you know your guns!


I'm particularly interested in long range artillery like the K5 and the Paris Gun before it.

I think the article is wrong. The barrel was rifled, and the splines engaged into it.


Well spotted. Worth pointing out that there was however the K5 Glatt smoothbore version bored out to 31cm that fired an FSDS round suspiciously similar to Soviet post war tank ammunition.

This was the Peenumünde arrow shell - Peenemünder Pfeilgeschoss or Flugstabilisierte treibringgeschoss. It was of 12cm caliber and 1911mm (75.23 in) long, with a 31cm diameter three-piece discarding ring sabot at the waist and four fins at the rear. ( some early model had six fins ) On firing, from the K 5 Glatt smoothbore gun, the ring was discarded and fell about 2km ( 1.25 miles ) in front of the gun, leaving the fin-stabilized projectile to fly to the target. development began in February 1940 and the long-range trials, fired at the Rugenwalde range, gave a maximum range of 151 km ( 93.83 miles )
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Unread postAuthor: Labtecpower » Wed Mar 30, 2011 8:01 am

Gardena quick connect stuff

The gun is a bit getto, but that was good enough for the teacher I sold it to.

Also, a question for tech:

Would increasing the bore diameter increase the muzzle velocity?

I'm talking about an increase from 4,6 cm to 7 cm.
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Unread postAuthor: jackssmirkingrevenge » Wed Mar 30, 2011 8:10 am

Labtecpower wrote:Would increasing the bore diameter increase the muzzle velocity?


Too many variables to answer that.

Imagine you keep the same valve and projectile weight, but double barrel diameter.

You now have 4 times the surface area for the air to push on, but as the projectile moves, barrel volume expands at a rate 4 times greater, so the valve might not be able to keep up with it.

As an extreme example, imagine a pneumatic launcher with a 3/4" QEV. With a 6mm barrel it will fire an airsoft BB pretty fast.

If you fit a 0.5" barrel and put the BB in a sabot, the air has a greater surface to push, yet the valve can still keep up, so with a lightweight sabot you would most likely get a significant performance increase.

If you fit a 2 inch barrel and put the BB in a sabot, you might not actually get an increase in performance, as there is now there is significant sabot weight to consider too, as well the increased barrel cross section which is much greater than that of the valve.

I suggest you have a play with GGDT to have a rough idea how these factors will actually affect performance.
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Unread postAuthor: Labtecpower » Wed Mar 30, 2011 8:17 am

GGDT predicts a 200 J increase in power, with the same projectile weight and a barrel of 230 cm.

Of course the valve isn't modeled as it should be.
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