A negative lead is typically used when engaging a stagnant target while the shooter is moving. A negative lead can also be used on a moving target.
Negative leads are typically seen in high-wind velocities, when the target speed is relatively slow. Let’s use the following as an example:
- A 175-grain .308 HPBT bullet
- Bullet velocity of 2650 FPS
- A wind velocity of 10 MPH at a 270° angle
- A distance to the target of 400 yards
Negative Lead Calculation
With the information provided above, in order to hit a stagnant target at this distance, we know that we will need a wind hold of approximately .91 MILs in the direction of the wind. If the target is moving at a speed of 4 MPH with no wind, the lead will be around 2.4 MILs. If the 4 MPH target is moving in the direction of a 10 MPH wind (left to right), we will need a lead of 1.7 MILs as opposed to the -3.5 MILs if the target was moving right to left. The reason for the drastic MIL hold is due to the fact that we are not only fighting the wind velocity, but the lead as well (when the target is moving into the direction of the wind).
With a wind velocity of 20 MPH moving the same direction of the target at 270°, we will need a lead of only 0.8 MILs. The lead value decreases because we are using the velocity of the wind to help ‘push the bullet’ into the moving target. The lead value drastically decreases when the wind’s velocity exceeds 30 MPH. So for a target speed of 4 MPH, moving left to right, with a wind velocity of 30 MPH at a 270° angle in relation to the shooter, we can expect a hold of around -0.1 MILs. For a target that is moving at a slow walking pace with the direction of the wind, blowing at 2 MPH, the lead hold would be -1.4 MILs.