Sectional Density is important because, all other variables being equal, a bullet with a higher Sectional Density will:
- Lose less energy and speed in flight
- Drop less on the way to the target
- Penetrate more effectively into a target
The M855 5.56mm bullet has a Sectional Density of 0.178. The 147gr 7.62mm NATO bullet has a sectional density of 0.221.
The bullet with the worst sectional density would be a round ball.
The heavier and more narrow the bullet is, the higher its sectional density will be.
If the 7.62mm bullet above weighed 150 grains, it would have a sectonal density of .226. If it weighed 165 grains, it would have a sectional density of .248.
Bullets of the same diameter and weight may have different sectional densities if they are made of different materials, such as depleted Uranium.
Not all bullets with the same weight, diameter, and sectional density perform the same. Bullet shape can significantly effect performance.
Sectional Density is abbreviated SD.
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