Is dispersion growing?

Dispersion is the phenomenon of dispersion of bullet impact points over a certain area (in a certain space) when shooting from the same weapon under practically identical conditions.

Many shooters have a deep-rooted belief that dispersion (accuracy) is directly proportional to distance, but this is a false statement!

If your weapon provides a stable accuracy of 0.75 MOA, which is equal to a group diameter of 2.17 cm at 100 m, this does not mean that at 800 m your accuracy will remain within 17.4 cm (0.75 MOA).

This is explained by the fact that the dispersion depends no longer on the angular error, but is determined by the transverse component of the bullet velocity, and the deviation will be proportional to the bullet’s flight time.

I would like to emphasize that the above factor is the most important and significant, but not the only one in this matter, and for those readers who want to delve deeper into the topic, we provide a direction for research, for everyone else we offer B. Litz’s formula, by which you can calculate the characteristic accuracy for your weapon system and ammunition at various distances.

All you need to is to multiply the accuracy in cm per 100 m by the bullet’s flight time (at the required distance), and then divide by the flight time per 100 m.

Example: Caliber 338 LM, Hornady HPBT 250 gr (G7 – 0.315). Velocity 884 m/s under standard weather conditions.

Let’s assume that this ammunition for our weapon gives a stable accuracy of 1 MOA (2.9 cm) at a distance of 100 m, and we need to calculate the dispersion at 1000 m.

The data from the ballistic calculator give us a flight time at 100 m of 0.116 s, respectively at 1000 m – 1.574 s.

2.9 cm × 1.574 ÷ 0.116 = 39.35 cm.

The dispersion at 1000 m will be 39.35 cm.

How does it work?

In simple terms, the flight time depends on the initial (muzzle) velocity and the ballistic characteristics of the bullet: The higher the speed and the higher the BC (ballistic coefficient), the better the bullet penetrates the air and, accordingly, reaches the target faster. This means that the factors that affect the accuracy act on the bullet for a shorter time, and thus deviate it less from the ideal trajectory.

This formula is not 100% accurate due to deterministic variables, primarily wind or the second factor – variations in muzzle velocity, but it works.

Happy hunting, Gentlemen!