Method
When Eötvös accommodation becomes a practical need (such as with an SF Spotter in a HVT environment), calculation may be avoided in most cases involving human-sized targets without compromising reliable shot placement.
In these instances, estimated corrections are most effectively communicated with hold off values, or designating altered points of aim.
Value estimation
The Eötvös effect is a directional factor that shifts point of impact vertically. Due to its directional nature, no displacement is seen when firing directly north or south. Vertical deflection gradually increases as our direction of fire shifts towards the East or West, with a maximum deflection when shooting straight east or west.
To guide estimation and better determine under which conditions the Eötvös effect becomes relevant, rough values for Eötvös deflection are provided below:
| East (Max) | NE, SE (Moderate) | West (Max) | NW, SW (Moderate) | |
|---|---|---|---|---|
| 600m | .06 MRADs Higher | .04 MRADs Higher | .06 MRADs Lower | .04 MRADs Lower |
| 800m | .08 MRADs Higher | .06 MRADs Higher | .08 MRADs Lower | .06 MRADs Lower |
| 1000m | .12 MRADs Higher | .08 MRADs Higher | .12 MRADs Lower | .08 MRADs Lower |
| 1100m | .14 MRADs Higher | .1 MRADs Higher | .14 MRADs Lower | .1 MRADs Lower |
| 1200m | .15 MRADs Higher | .11 MRADs Higher | .15 MRADs Lower | .11 MRADs Lower |
Example 1
Sgt McShooty is deployed as an SF Spotter. He ranges his HVT at 1000m. Needing to guarantee shot placement, he measures the target azimuth at 90°, straight East. Firing towards the East will raise point of impact.
After providing the SF Sniper with a ballistic solution, he designates an altered point of aim to accommodate for the Eötvös effect:
“Aim 6 O’clock, belt buckle"
Example 2
Sgt McShooty is deployed as an SF Spotter. He ranges his HVT at 800m. Needing to guarantee shot placement, he measures the target azimuth at 315°, directly Northwest. Firing towards the West will lower point of impact. Firing to the Northwest decreases this effect.
After providing the SF Sniper with a ballistic solution, he designates an altered point of aim to accommodate for the Eötvös effect:
“Aim 12 O’clock, shirt collar”
Limitations:
The height of human targets (as compared to their width) allows us a margin for error, and permits the relatively small deflection of the Eötvös effect to be estimated with reliable success. Should the height of our target no longer be as forgiving, such as in the case of an obscured target, estimation of the Eötvös effect will no longer be a reliable method for achieving guaranteed shot placement.
The provided values for Eötvös deflection assume an average latitude for all of our campaigns (38.5*) and do not account for atmospheric conditions. A 7.62 NATO cartridge has been assumed for the needed time of flight values. While this method will serve well in most scenarios, it should be noted that map latitudes or bullet times of flight deviating greatly from the data used can produce drastically different effects downrange.
