the muzzle engery is the same (more or less) so the rock vs pebble doesnt work out..
its all about watts, aka engery over time.. and the FPS makes the difrance as we are talking about how fast the engery is transfred
if i stand chest to chest(as in touching) with you, put my fist on your chest and push with all I can, I will shove you back, but it won't really hurt much.. now if I stand 2 feet away and punch you in the chest with the same about of force its going to hurt.. even tho the engery is the same, the punch delivers it in a shorter time span
lets look @ a point blank shot form a 1 J gun
a .12 is flying(numbers rounded) 1290 cm/s and a .43 is 680 cm/s
lets say the engery is transfred over 1cm of inpact in to the skin
the .43 transfers 1 j in .00147 sec for an impact of 680.272 watts
the .12 transfers in .00075 sec for an impact of 1333.333 watts
the lighter faster round does more damage do to the speed.. things flip flop down range as the light round losses engery quicker.
throw numbers out the windo, heres a real world look @ the efect
***opens note book***
Demonstration of increased penetration form the same muzzle energy, caused by less mass and more speed.
Test platform CM030 @ 4", last crony 183-185 w/.2s
Test media- 2 sheets of Styrofoam
Ammo-Excel .25s and cheep .12s that have been rolling around in my trunk for years , (what do you want I havenít owned a gun that takes .12s for years ;-)
First photo, the 2 sheets stacked showing the top of the 1st sheet, entrance holes clearly visible, you can see the pencil zip tied to the gun as a standoff to keep the distance the same for all shots.
Second photo, the bottom of the 1st sheet. The .12s broke threw in all 4 shots and are visible in 2 cases, kept going in 2 cases and were caught between the sheets.
The .25s did not break threw but did deform the back side of the foam in 3 cases, in one case it left no disturbance on the back side.
Top of the second sheet, 3 dents form the .12s can be seen. The .25s left no marks on the second sheet.
In an ideal would I would have put all the shots across a crony so were could be sure the energy levels were the same and the .12 do to the short barrel were getting more energy then the slower .25
But either way the results seem to be imperial data that in many cases, @ close range, lighter faster ammo has more penetration.