Myth – “Even though the group isn’t centered I don’t want to adjust the sights because I already have a zero.”
Fact – A zero is only as good as the placement of each correctly called shot.
FM 3-22.9, Page 5-21
“KD Zeroing. The 300-meter target can be used at 300 meters to confirm weapon
zero or to refine the zero obtained on the 25-meter range. The zero on this target is more valid than the zero obtained on the 25-meter range . . . Soldiers should fire two 5 round shot groups to confirm zero or three-round shot groups to refine their zero.”
The term “zero” implies no deviation from the point of aim to the point of impact. Because line of sight is straight and the trajectory is not zero is used in reference to a number of different things:
- Mechanical – physically centering the sights
- No Wind – windage setting for a given lot of ammo, disregarding environment
- True – specific sight setting for a specific shot in a specific environment
- Battle (BZO) – no wind setting that allows the shooter to ignore the distance to a target of a certain size just beyond the distance zeroed for.
Differences in environment (temperature, air resistance, altitude), ammunition lots and other factors can yield a zero change. Provided you fired and called a good group, never be afraid to make adjustments. This assumes you can accurately call each shot . . .