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According to Richard Middleton's book, "ManPowered Weapons and Ammunition", page 75; the speed of a projectile is inversely proportional to the cube root of its mass.
He points out that when calculating for a slingshot we must weigh the rubber and the pouch and add the result to the projectile.
My data is:
16 grains 220 fps
80 grains 200 fps
224 grains 165 fps
Using the attached spread sheet, I added a column for the weight of the rubber and the pouch.
What I found was that I could only match 2 adjacent data sets as I plugged in various values.
I could calculate 220 and 200 or 200 and 165, but never all 3.
It appears that my Red TB tube has a velocity of a little more than 220 fps.
Going up from 16 grains to 80 grains reduces the speed only 10%
Going up from 80 grains to 240 grains reduces the speed 17.5% more.
Any ideas why it does not scale according to theory?
He points out that when calculating for a slingshot we must weigh the rubber and the pouch and add the result to the projectile.
My data is:
16 grains 220 fps
80 grains 200 fps
224 grains 165 fps
Using the attached spread sheet, I added a column for the weight of the rubber and the pouch.
What I found was that I could only match 2 adjacent data sets as I plugged in various values.
I could calculate 220 and 200 or 200 and 165, but never all 3.
It appears that my Red TB tube has a velocity of a little more than 220 fps.
Going up from 16 grains to 80 grains reduces the speed only 10%
Going up from 80 grains to 240 grains reduces the speed 17.5% more.
Any ideas why it does not scale according to theory?
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