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Old 12-22-2017, 09:51 PM
mmartin798 mmartin798 is online now
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Location: Michigan
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Default Proposed change for range affect on damage

On page 88 of the 4th edition rules there is a section entitled "Range Effects on Damage" which outlines how E-factor diminishes with range. In short, the rule states that damage falls by 1 for every multiple of effective range. As is often the case, this didn't sound right, so I went to the spreadsheet and plotted the rule against the results from GNU Ballistics for three different rounds. The results are shown in the top picture entitled "Range vs EFactor-Current". The rule results are plotted in green while the GNU Ballistics results are in blue. It is pretty obvious that they do not match up very well. Also, contrary to the rest of text in the "Range Effects on Damage" section of the rules, the heavier rounds were not necessarily affected more. The lightest round in the sample was the 5.56mm. If you look the 9mm is much flatter than the 5.56mm showing the exact opposite of the regarding mass of the round. Fortunately this rule has a relatively easy fix, but to understand it, the GNU Ballistic plots need to be looked at in more depth.

If you look at both the 5.56x45mm and 12.7.99mm rounds, the pattern of the blue dots in both cases is very much a hockey stick. The 9x19mm is pretty flat. That is because the speed of sound is about 1100 f/s. That almost the initial velocity of the 9x19mm round. Looking at the 5.56x45mm and 12.7x99mm rounds the point where the curve flattens out happens around a velocity of 1100 f/s as well. From this we can assume that it is the faster than sound velocity that dramatically increases the drag. Again, comparing the 5.56 and 12.7 we see that the velocity drops to sub-sonic after about 2 multiples of the effective range and that the damage drops by about 1/3 of the range zero EFactor. This is a good start.

Looking at the 9x19mm plots, the rules drop off damage much too quickly. You get a much better fit if you drop the damage by 1 every 2 multiples of effective range.

Combining these two new findings to the rules column and plotting them against the GNU Ballistics result gives the results you see in the bottom picture entitled "Range vs EFactor-Proposed". These curves match up much better and the rules are still easy to apply.
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