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Discussion Starter · #1 ·
For those without a chrony this just might be of interest:

http://www.pyramydai...splatology.html

It's a reference created by Gary Barnes to to estimate air gun velocities but it's very applicable to slingshots. A lead ball of any calibre will give the same mushrooming when fired at a hard surface at a particular fps.
I cross checked it using some 00 buckshot fired with tapered 1745 tubes which give a consistent 300-325fps with my standard draw.
Well suprise suprise It actually works!! Not quite an F1 chrony but I think it"s a little gem.

Here's some 00 buck staring to pancake post firing at a sandstone wall at 310-315 fps (on a 20 degree angle to avoid a ricochet!).
It correlates quite neatly with the chart.

IMG_32061.JPG
 

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This is very interesting, and certainly warrants further investigation. There are a number of complicating factors that I can see right off the bat.

First, the degree of deformation will depend significantly on the exact metallic formulation. A lot of my ammo comes from wheel weights, which have a high tin content. Consequentlly they are harder than pure lead and will not splat in the same way.

Second, slingshot velocities are mostly less than 250 fps. I doubt that I have ever fired a slingshot projectile more than 250 fps. The deformations discussed in the article are for velocities greater than 250 fps, so not of great use to slingshot enthusiasts.

Perhaps one could do some standardized test with pure lead balls of known diameter against a steel splash plate. The resulting diameter across the flat and dome should give a pretty accurate indication of velocity. Just something to consider.

I have thought of using a penetration test. Set up layers of standard weight office bond in a rigid frame. I suspect that velocity would be clearly indicated by the number of layers that could be penetrated by a ball of a specified standard size and mass. Start with say 5 layers, then go to 6, then to 7, etc. until you find a thickness that the ball will not penetrate. I recall as a boy reading about penetration tests for .22 ammo (and others), using 1/2 inch pine boards, and that is what gave me the idea.

Anyway, thanks for pointing this out to us!

Cheers ....... Charles
 

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Discussion Starter · #4 ·
Thanks Charles.You raise some pertinent and valid points. Certainly there may be some variability in the hardness of buckshot/sinker balls/home poured lead balls in comparison to the lead used in this chart. Most definitely the amount of antimony added to lead shot will affect hardness.
You also correctly point out it isn't applicable below 250fps.
Despite this there are alot of us that don't mind the expense and time cutting bands to attain the pleasure of high speed shooting and for this cohort the Barnes chart has some value.
 

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Thanks Charles.You raise some pertinent and valid points. Certainly there may be some variability in the hardness of buckshot/sinker balls/home poured lead balls in comparison to the lead used in this chart. Most definitely the amount of antimony added to lead shot will affect hardness.
You also correctly point out it isn't applicable below 250fps.
Despite this there are alot of us that don't mind the expense and time cutting bands to attain the pleasure of high speed shooting and for this cohort the Barnes chart has some value.
Absolutely agree with you. It always seems that when Aussies report velocities, they are much higher than mine!!! Part of it has to do with your higher temperatures, no doubt ... sort of like heating the bands. Certainly for folks shooting at those high velocities (250+ fps), it represents a pretty quick and dirty check on velocities.

Cheers ....... Charles
 

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Well them balls sure were moving, I myself not long ago posted pics of a 300+fps pancaked shot compared to a mid 200fps shot, and the difference definitely shows... good find mate...
And referring to our weather, despite popular belief, its not always 30 plus degrees c in Australia, and I doubt the weather plays THAT much difference, as in 100fps difference between our, and some milder climates.. its more how ya do it
 

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This is very interesting, and certainly warrants further investigation. There are a number of complicating factors that I can see right off the bat.

First, the degree of deformation will depend significantly on the exact metallic formulation. A lot of my ammo comes from wheel weights, which have a high tin content. Consequentlly they are harder than pure lead and will not splat in the same way.

Second, slingshot velocities are mostly less than 250 fps. I doubt that I have ever fired a slingshot projectile more than 250 fps. The deformations discussed in the article are for velocities greater than 250 fps, so not of great use to slingshot enthusiasts.

Perhaps one could do some standardized test with pure lead balls of known diameter against a steel splash plate. The resulting diameter across the flat and dome should give a pretty accurate indication of velocity. Just something to consider.

I have thought of using a penetration test. Set up layers of standard weight office bond in a rigid frame. I suspect that velocity would be clearly indicated by the number of layers that could be penetrated by a ball of a specified standard size and mass. Start with say 5 layers, then go to 6, then to 7, etc. until you find a thickness that the ball will not penetrate. I recall as a boy reading about penetration tests for .22 ammo (and others), using 1/2 inch pine boards, and that is what gave me the idea.

Anyway, thanks for pointing this out to us!

Cheers ....... Charles
well Charles
you read my mind but put it eloquently! in my wurds........ tu miny varibls?
 
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