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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: POLAND_SPUD » Sat Apr 23, 2011 4:44 pm

Yeah I know... when I said
Cg and Cp must be pretty much in the same place...

I meant your projectile
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Unread postAuthor: drex » Sat Apr 23, 2011 5:03 pm

ah, I'm going to make a new one with a polycarbonate body and fins, and a steel nose cone it should do much better.
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Unread postAuthor: POLAND_SPUD » Sat Apr 23, 2011 5:21 pm

if it works for shotgun slugs...
http://www.thefirearmblog.com/blog/2010 ... gs-part-7/

then it should work with spudguns


I couldn't find anything about drag stabilised rockets, but I think I know why...
the motors reduce base drag (which is why base bleed artillery shells exist ;-) )
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Unread postAuthor: dewey-1 » Sat Apr 23, 2011 8:59 pm

drex wrote:


the cp needs to be at least one body width below the cg to be considered stable.




Here is a quick drawing for nominal CG .
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Unread postAuthor: drex » Sat Apr 23, 2011 9:12 pm

what program did you use for that drawing and cp/cg calculations?


LeMaudit wrote:Any tip to share for removing the static? incantations? miracles?
the wife didn't see the mess yet... somebody??

humidifying the air? I don't have much trouble with static from UHMWPE where I work (south carolina).
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Unread postAuthor: shardbearer » Sat Apr 23, 2011 10:29 pm

Why are we all using sabots? Wouldn't a dart like this with a o ring in the middle be best, reducing weight and friction, and giving a better seal?
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Unread postAuthor: JDP12 » Sat Apr 23, 2011 10:30 pm

the idea of saboting a smaller round into a larger barrel is to give a larger kinetic energy density on target- with a larger barrel you get more KE transferred to the projectile, and the smaller diameter of the projectile results in better penetration on target, assumin the projectile is hard enough.
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Unread postAuthor: MrCrowley » Sat Apr 23, 2011 10:42 pm

Also, as seen by JSR's GGDT calculations, a 20mm projectile with the same mass and Cd value as a 40mm projectile will go as much as 3x further in distance due to sectional density.
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Unread postAuthor: jackssmirkingrevenge » Sat Apr 23, 2011 11:40 pm

drex wrote:I made this at work earlier this week I had a little bit of time to kill. the nose cone part is 1.250" and the tail part is .750" with a .5 inch id. it did tumble so it was not a success in that regard, however the sabot did separate quite nicely.


Shame about the projectile not working but great sabot, there's certainly potential for development.

shardbearer wrote:Why are we all using sabots? Wouldn't a dart like this with a o ring in the middle be best, reducing weight and friction, and giving a better seal?


As explained above, higher velocity and better aerodynamics.

When the military want to lob a large quantity of explosives over a short distance, they use that kind of design:

Image

When they want to throw something fast and far (POLAND_SPUD, I hate living up to your expectations :D) they use something like this:

Image

LeMaudit wrote:Any tip to share for removing the static? incantations? miracles?
the wife didn't see the mess yet... somebody??


We have one ofthese at work, bit pricey though. You could also move to Europe where it's a bit more humid ;)

Looks like it is snowing inside the workshop :lol:
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Unread postAuthor: dewey-1 » Sun Apr 24, 2011 11:07 am

drex; I use an old 5 year AutoCad.

Here is the sabot with individual weights if I calculated them properly.
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Unread postAuthor: jackssmirkingrevenge » Sun Apr 24, 2011 1:03 pm

Impressive work Duane. You're right, as it is the weight is far too high. The material needs to be thinned out and drilled out :)
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Unread postAuthor: drex » Sun Apr 24, 2011 6:42 pm

Would a sobot like this work? it seems to me it would be easer to make and lighter.
Image

The only downside to this idea is it's less badass compared to a sabot that breaks into multiple parts.
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Unread postAuthor: JDP12 » Sun Apr 24, 2011 6:50 pm

that type WOULD work.. but any air irregularities the sabot would encounter would be transferred to the projectile, the advantage of a multipiece one is that they separate instantly on contact with air and separate away from the projectile in a circular way..

If that makes sense.
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Unread postAuthor: jackssmirkingrevenge » Sun Apr 24, 2011 10:22 pm

drex wrote:Would a sabot like this work? it seems to me it would be easer to make and lighter.


I like it! My only objection is the length of the rod which lengthens separation time.

I would make it like this, with full bore fins. That way, the sabot is lighter, the projectile is more dense and also more aerodynamic due to the pointy tail.
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Unread postAuthor: mobile chernobyl » Sun Apr 24, 2011 10:25 pm

I've used this design before on a few distance darts I made. It does indeed work very well - so long as the front of the dart is not heavy enough to cause deflection in the fins to the point where it can lay lop sided in the barrel. Even then the drag stabilization of the fins kicks in pretty fast to straighten things out mid flight if their adequate.
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