Vortex Optics VIPER HS LR 6-24X50 RIFLESCOPE — First Focal Plane - Manual (Page 3)

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MOA Subtensions
The XLR reticle is based on minute-of-angle (MOA) subtensions.
MOA measurements are based on degrees and minutes: 360 degrees
in a circle, 60 minutes in a degree for a total of 21,600 minutes. These
angular measurements are used to estimate range and correct for bullet
trajectory drop in riflescopes. 1 MOA will correspond to 1.05 inches at
a 100 yard distance, 2.1 inches at 200 yards, 3.15 inches at 300 yards,
and so on.
First Focal Plane Reticles
When used in a first focal plane riflescope, such as this Vortex Viper
HS LR riflescope, the MOA subtensions of the XLR reticle are
valid at all magnification levels. This means the shooter can use the
magnification level most appropriate for the situation and still have
effective holdover and windage reference marks.
This is extremely valuable in a high-stress situation because the
shooter does not have to remember to set the scope to one particular
magnification to get valid holdovers—an action necessary in the more
common second focal plane reticles.
Estimating MOA
Although 1 MOA is very commonly corresponded to 1 inch at 100
yards, this is not quite correct 1 MOA at 100 yards equals 1.05 inches.
Calling 1 MOA an inch per 100 yards may be acceptable at shorter
distances, but it will cause a five percent error in ranging and holdover
adjustments. This will result in missed shots at longer distances.
Viper XLR Reticle
Model A B D1 D2 D3 S X1 X2 X3
2.5–10x32 2.00 .21 .24 .33 .20 .6 2.0 1.0 2.0
4–16x50 3.13 .15 .26 .39 .15 .45 1.0 .5 2.0
6–24x50 2.08 .10 .17 .26 .10 .3 1.0 .5 2.0
XLR Reticle Subtensions (MOA)
A
B
X1
X3
∅ D2
X2
∅ D1
S (open center)
∅ D3 (center dot)