View Single Post
Old November 5th, 2008, 02:14   #51
DonP's Avatar
Join Date: Jul 2002
Location: Edmonton, AB
OK, a quick recap. The question I posed myself (and you fellows) was "All other things being equal, would loading lighter ammo into the same gun cause less of an ouch?"

A practical application of this would be loading a gun (like a sidearm) with .12g BBs in order to make it more CQB-friendly. Could this be reasonably expected to help?

It seems some people think yes (heavier ammo = more energy = more ouch), some people think no (lighter ammo = higher FPS = same energy), and some people like to argue.

Well, nothing gets the brain working like a good experiment.

Disclaimer: I did specifically lay out that this was half-assed science time.

My hypothesis: Lighter ammo will overall transfer less energy, compared to heavier ammo from the same gun.

The test setup: Putty is used as a way to capture and visualize BB energy transferred. Shoot the putty from point-blank ranges with a variety of BB weights (.12g, .20g, .28g, .30g) from a variety of guns. Measure the results with a depth gauge, and eyeball the hole.

Why do it this way:
Three main reasons:
  • The putty deforms when hit, and "freezes" when no more energy is spent deforming it. This is easy to measure and seems to be a consistent measure of energy transferred. As a side note, energy transfer should be optimal since the BB stays in full contact with the putty until it is no longer penetrating (energy transfer being a function of how long something can stay in contact over how much area, and all that. No glancing shots, etc.)
  • It therefore doesn't matter that putty doesn't act like skin, or that skin in different spots feels pain differently. We're interested only in relative energy between different weight BBs from the same gun. As long as it's consistently measured, we're good.
  • Shooting things that do something when you shoot them is fun.

Assumptions, Out Of Scope, etc:
  • In all individual tests: Same gun, same propellant, same putty, same range.
  • We are not measuring quantative energy, just relative energy between different weight BBs from the same gun. So converting "size of dent" into "joules" or whatever isn't in scope.
  • The bigger/deeper the hole in putty, the harder the hit.
  • The harder the hit, the bigger the OUCH potential.
  • Only point-blank ranges are tested. Results valid at point-blank will be valid at longer ranges since it's impossible for a BB to go faster the further it goes.
  • In other words, if a .12g BB doesn't hit as hard as .20g at point-blank, it never will no matter what range you go out to.
  • How well energy is retained at longer ranges for different weights is out of scope. (Meaning whether .20g retains energy better at longer ranges than .12g is out of scope.)


This is a typical target:

First up is a KJW 1911 Gas Blowback on duster at point-blank range (2m). NOTE THAT THE WHITE SPOTS INSIDE THE HOLES ARE PAPER FRAGMENTS. BBs DID NOT PENETRATE.

Observations: There is a clear progression in penetration depth related to BB weight.

Next is the same KJW 1911 Gas Blowback, but this time with a CO2 magazine.

Observations: The relation of penetration to BB weight is still clear. Overall all BBs penetrated further. The CO2 mag was observed to shoot noticeably harder.

Next up is a KJW MK1 Non-blowback on duster.
The non-blowback should fire the BB with a fixed "gas charge" unlike a GBB which keeps the gas on as long as the BB is in the barrel. This surely has some kind of effect on BB fps, but that's not specifically of interest here -- does a NBB versus a GBB change the trend we're observing?

Observations: Same progression observed -- more BB mass means more observed putty penetration.

Finally we have an APS2 bolt-action spring rifle.

Test 1 Observations: All BBs except for .12g penetrated into the backstop. Clearly .12g had less energy, but what about the rest?

Another test was done, this time with BDU material in front of the putty instead of a paper target.

Observations: Same trend observed as all previous tests. Heavier weight from same gun = more penetration.

Two decimal places of measurement for a depth gauge into putty smacks of "measure with micrometer, mark with chalk, cut with axe." This is not lost on me. So I did a quick test where I shot the putty with 4 rounds of .20g and measured each. The measurements were remarkably consistent; biggest deviation was .12mm. Admittedly it's a small sample size (just like the rest of this experiment) but it looks like putty is not only consistent but the depth gauge is as well. At least, enough to see what I'm trying to see.

  • Heavier BBs (i.e. more mass) fired from the same gun equals more energy transfer on impact. (Compared to lighter ammo)
  • Lighter BBs (i.e. less mass) fired from the same gun equals less energy transfer on impact. (Compared to heavier ammo)
  • The different mechanics of operation between a NBB versus a GBB versus a spring piston doesn't change this.
  • Shooting stuff is pretty fun.

Therefore, while pain is subjective and depends on where and how one is shot, I think it would be reasonable to explore loading .12g BBs into a gun for the purposes of making it more appropriate for CQB - for example into a gas gun sidearm which otherwise might shoot pretty hot. (And CQB is an environment where the poor accuracy of .12g at range won't be much of an issue.)

Whether it actually makes enough of a practical difference to make a hot gun safer? Maybe!

Last edited by DonP; November 5th, 2008 at 02:51..
DonP is offline   Reply With Quote