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Old November 5th, 2008, 02:59   #55
Delierious Designer of Dastardly Detonations
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Join Date: Dec 2001
Location: in the dark recesses of some metal chip filled machine shop
I'm guessing that the putty behaves incompressibly when it deforms so some sort of flow has to occur to create a bb crater. Given the flow-velocity issues I would think that it would be best to take the backstop out of the behavior and have the putty flow uninfluenced by a rigid backstop which imposes some funny shear behavior right at it's face. I would think that this factor would exacerbate the non Newtonian behavior of the putty.

I've been guessing that equivalent energy for different weight pellets would have the same potential for doing work when they smash into things. I suppose the only other absorption for energy (other than deformation) could be heat which could be significant for viscous media like putty which does transform a fair bit of work into heat when you knead it. I don't know how the heat issue translates into pain factor, but it's hard to measure the temperature rise in the immediate impact area and this would be unaccounted energy.

I've found AEGs to be largely constant energy devices, but when shooting very low weight pellets this behavior starts to break a bit (IRC it's been a really really long time since I did this battery of tests). I suspect that very light pellets offer such a low resistance to flow that other restrictions and the piston mass start to eat up more energy. This is why I suggest measuring impact fps. Also it does help to throw out the odd hot shot.

Now that I think of it, quantifying damage potential is a very difficult problem. The influence of speed and penetration are pretty well documented. At some point very very fast projectiles cause cavitation and end up destroying themselves in most ballistic media while slower heavier masses can achieve much deeper penetration. Our dinky balls operate in a completely different velocity regime, but I think it's hard to determine an accurate correlation between penetration and pain without using a media which actually simulates human flesh. I'm starting to come to a better appreciation of why the FBI chose ballistic gelatin because it offers a good analogue to tissue to assess penetrating damage.

In our very low energy situation with light projectiles, I think we need to choose a medium which is significantly less dense than our projectiles. It's obvious that dense media will significantly slow faster less dense projectiles with flow resistance, but I argue that this is not a good indication for low pain since our projectiles usually don't enter into the body and experience surface flow resistance.

I'm thinking we need a hybrid target that behaves in a Newtonian manner with an unpenetrated skin (like your cloth outer). Maybe a foam target that isn't resiliant with a cloth outer might be a good target. It would exhibit low rate dependent behavior and still provide a permanent deformation to assess. Maybe put a canvas cloth on that green sponge that flowers get stuck into.
Want nearly free GBB gas?

Last edited by MadMax; November 5th, 2008 at 03:01..
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