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Punkin Chunkin 2010 Mythbusters Episode

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: saefroch » Sun Nov 28, 2010 11:58 am

While such a research organization probably has access to better resources than most punkin chunkin teams, I'll take your word that it can be done.

So assuming you've got a captive piston, couldn't you make something like a springloaded "pumpkin cushion" to act as a shock absorber and allow greater acceleration of the sabot at launch? The spring would probably also extend when the sabot is caught, returning a good portion of its energy to the pumpkin...
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 28, 2010 12:13 pm

saefroch wrote:So assuming you've got a captive piston, couldn't you make something like a springloaded "pumpkin cushion" to act as a shock absorber and allow greater acceleration of the sabot at launch? The spring would probably also extend when the sabot is caught, returning a good portion of its energy to the pumpkin...


That would definitely make sense, here's how I would make it...
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Unread postAuthor: saefroch » Sun Nov 28, 2010 12:19 pm

So you're increasing the area of the barrel (and thus force on the sabot) by a factor of what now?

Dang, with a design like that, spudfiles should enter a build next year.
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Unread postAuthor: Gun Freak » Sun Nov 28, 2010 12:26 pm

saefroch wrote:Dang, with a design like that, spudfiles should enter a build next year.

We would totally win :D
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Unread postAuthor: Technician1002 » Sun Nov 28, 2010 1:38 pm

My piston (sabot) was not captive, but the results are impressive. AA batteries launched from a 1/2 inch barrel on a 1 inch valve vs a sabot and 2.5 inch barrel on a two inch valve show the potential.

This thread has info and more photos of my sabot AA battery shot on page 2.
http://www.spudfiles.com/forums/flat-aa-battery-i-challenge-some1-to-replicate-this-video-t21827,start,15.html

1/2 inch barrel at 100 PSI
Image
vs about 65 PSI and the 2.5 inch barrel.
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 29, 2010 1:27 am

Gun Freak wrote:We would totally win :D


Totally :)

Tech wrote:My piston (sabot) was not captive, but the results are impressive. AA batteries launched from a 1/2 inch barrel on a 1 inch valve vs a sabot and 2.5 inch barrel on a two inch valve show the potential.


While it can be a pain to put together, the advantages of using a sabot can be condensed into the following:

- low sectional density in the barrel, meaning that much higher acceleration is possible than a full bore projectile

- high sectional density outside the barrel (for the projectile), meaning lower deceleration in flight and higher penetration

To give an illustration of the extent of the difference, here's some data for the British 17 pounder gun (with penetration in millimetres at various ranges):

Ammunition Weight Muzzle Velocity 500 yards 1000 yards 2000 yards

APCBC 17lb 2900fps 140 131 111

APDS 7.625lb 3950fps 209 192 161

As you can see, the discarding sabot projectile weight is significantly lower, however the velocity at the muzzle is over 1000 fps higher and there is a corresponding increase in penetration, to the extent that at 2000 yards it penetrates better than the full bore at 500 yards. The rounds being compared are the bottom two in this diagram:

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