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shape of projectiles (Read 1771 times)
graf_zahl
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shape of projectiles
Feb 18th, 2005 at 2:43am
 
i want to cast my own projectiles, but i don't know which shape i should chose - spherical oder biconical? can somebody explain me the advantages of each variation?
i want to make them with a weight of 65g - to less, to much or right? my sling has an length of 1m (netted).
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« Last Edit: Feb 18th, 2005 at 3:56am by graf_zahl »  

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mgreenfield
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Re: shape of projectiles
Reply #1 - Feb 18th, 2005 at 10:42am
 
This is a big question.  First figure out what sling length, slinging style and ammo weight you're most comfortable with, then make ammo to fit that preference.

Style is grip-type (wide vs narrow), plus delivery method (overhand, underhand, sidearm). 

Lots of postings here on all this.   mgreenfield
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Matthias
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Re: shape of projectiles
Reply #2 - Feb 18th, 2005 at 3:28pm
 
Much depends on whether or not you can accurately control the launch attitude and spin of your projectile. Spheres will probably be the most forgiving. If you can achieve constistent point first flight, moving to more aerodynamic shapes should net you some big gains. In general, for subsonic ammo, you want to stay away from sharp points etc. If your handle is Techstuf, your results may vary...

The following table uses commonly reported values for the drag coefficient and takes into account the effect of smaller frontal area for ellipsoids of varying aspect ratios. Note that you get a double benefit with the streamlined shapes - for a given weight, not only is the Cd lower but the glans has to push less air aside due to the smaller diameter.

...

In "real life" half a dozen other effects come into play. Surface finish, lift due to spin, lift due to shape, and change of attitude during flight are big ones. For practical slinging, handling in the pouch and stability in flight will be important too.

My "concept" glans shown above holds to 2:1 ellipsoid shape. The surface is a smooth as practical, but there is ring of "turbulators" on the nose to encourage a turbulent boundary layer. The tail is truncated to creat a sharp edge in the hopes of additionaly controlling the wake seperation point. Do any of these tricks work? Who knows! Additional testing to follow Wink

I'll wait for someone else to figure out how almond shaped ammo works Grin

Matthias
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TColorSling11
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ERIE SLINGER

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Re: shape of projectiles
Reply #3 - Feb 18th, 2005 at 3:34pm
 
almond,  i gotta dry that, brobably would be a waste of time, you be better off sticking to thelong ovals
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TColorSling11
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ERIE SLINGER

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Re: shape of projectiles
Reply #4 - Feb 18th, 2005 at 3:35pm
 
TRY**
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Yahweh Bless you in Yeshua
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Re: shape of projectiles
Reply #5 - Feb 18th, 2005 at 5:04pm
 
Matthias is correct.....Spheroid ammo is most forgiving.  Part of the reason I use it almost exclusively for target sport.  Smooth surfaced ball ammo works quite well here.

As for distance slinging,  I prefer darts.

I myself, do not have a dedicated interest in engineered ellipsoid ammo,  and I would certainly accede to your numbers, Matthias.

(No need to fire up the 'hot air windtunnel' here.  Wink )

Matthias, your general statement regarding points is certainly valid as well.  I have borrowed from the archery manufacturing community in my efforts and found that some 'points' provide quite acceptable subsonic performance......particularly those made by Saunders Archery Company.  

...

The drag increase resultant from an increased bow wave diameter is largely mitigated by smaller body diameters and avoiding angularity.

Of course, this is not to say that there are not ways to eke out more distance using creative 'short body' geometry!  There is certainly a largely unexplored frontier here.....and exploiting high RPM spin characteristics aerodynamically seems to show promise.

Your 'turbulator' ammo is certainly eye catching......the addition of the 'turbulators' reminds me of one of Nerf's later football efforts!  There is also some resemblence to a few 'Boat-tail' bullets I have seen.

I would imagine that perhaps a decent market may be established for production line ammo of such a sort....

Smiley
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« Last Edit: Feb 19th, 2005 at 2:44pm by Yahweh Bless you in Yeshua »  

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TColorSling11
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ERIE SLINGER

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Re: shape of projectiles
Reply #6 - Feb 19th, 2005 at 2:27pm
 
ummm
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graf_zahl
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Re: shape of projectiles
Reply #7 - Mar 8th, 2005 at 10:13am
 
i want to try some clay glands. i've seen many of different shapes and models, but i've never found some measures. could somebody tell me the measures of a gland with a weight about 40-60gr (dry clay)?
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