The
"Best"
Measure
of
Lethality
In a fascinating article posted at Thudscave.com titled "How
Hard Does It Hit?" by Daryl Hrdlicka, of the Jeffers Petroglyphs
Historic Site, analyzes three measures of weapon lethality: kinetic
energy, momentum, and sectional density.
At first glance it would seem that kinetic energy (1/2 mass x
velocity^2) is the most appropriate measure of a weapons power, and in
the general I will follow this approach. However it matters a lot
whether the projectile has momentum (velocity x mass) (to continue
moving through hide and muscle) and sectional density (mass/diameter^2)
to initiate penetration. He compares spears with the atlatl, the
arrow and the handgun. Two versions of each are used to set an
upper and lower boundary. Pounds, ounces and grains for
projectiles reflect the different usages of those who publish data on
various types of weapons.
I have taken the following data directly from his work and
compacted it into a single table.
Note:
| Weapon |
Weight
|
Weight
lbs
|
Velocity (ft / sec) |
Kinetic Energy
(ft. lbs) |
Momentum (slug ft / sec) |
Sectional Density (psi) |
| .30-06 Rifle |
180 grains |
0.0257
|
2600 |
2701 |
2.08 |
0.285 |
| .357 Magnum Pistol |
125 grains |
0.0178
|
1450 |
583 |
0.80 |
0.140 |
| Light Spear |
2 pounds |
2.00
|
73.5 |
167 |
4.57 |
2.000 |
| Heavy Spear |
5 pounds |
5.00
|
37 |
106 |
5.75 |
2.222 |
| Light Dart |
3 ounces |
0.0187
|
125 |
45 |
0.73 |
0.750 |
| Heavy Dart |
6 ounces |
0.0375
|
103 |
62 |
1.20 |
0.960 |
| Primitive Arrow |
500 grains |
0.0714
|
165 |
29 |
0.37 |
0.508 |
| Modern Arrow |
540 grains |
0.0771
|
220 |
58 |
0.52 |
0.653 |
1 lb = 16 ounces = 7000 grains / 1 ounce =
437.5 grains = 0.0625 lbs
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