Sight adjustment Milliradian

1 sight adjustment

1.1 common click values
1.2 subtensions @ different distances
1.3 adjustment range , base tilt

sight adjustment

example ballistic table given 7.62×51mm nato load. bullet drop , wind drift shown both in mil , moa.

mil adjustment commonly used unit clicks in mechanical adjustment knobs (turrets) of iron , scope sights both in military , civilian shooting sports. new shooters explained principle of subtensions in order understand milliradian angular measurement. subtension physical amount of space covered angle , varies distance. thus, subtension corresponding mil (either in mil reticle or in mil adjustments) varies range. knowing subtensions @ different ranges can useful sighting in firearm if there no optic mil reticle available, involve mathematical calculations , therefore not used in practical applications. subtensions change distance, mil (as observed through optic) mil regardless of distance. therefore, ballistic tables , shot corrections given in mils thereby avoiding need mathematical calculations.

if rifle scope has mil markings in reticle (or there spotting scope mil reticle available), reticle can used measure how many mils correct shot without knowing shooting distance. instance, assuming precise shot fired experienced shooter missed target 0.8 mils seen through optic, , firearm sight has 0.1 mil adjustments, shooter must dial 8 clicks on scope hit same target under same conditions.

common click values

general purpose scopes

gradations (clicks) of 1/4′, 1/10 mil , 1/2′ used in general purpose sights hunting, target , long range shooting @ varied distances. click values fine enough dialed in target shooting , coarse enough keep number of clicks down when dialing.

speciality scopes

0.25/10 mil, 1/8′ , 0.5/10 mil used in speciality scope sights extreme precision @ fixed target ranges such benchrest shooting. specialty iron sights used in issf 10 m, 50 m , 300 meter rifle come adjustments in either 0.5/10 mil or 0.25/10 mil. small adjustment value means these sights can adjusted in small increments. these fine adjustments not suited dialing between varied distances such in field shooting because of high number of clicks required move line of sight, making easier lose track of number of clicks in scopes larger click adjustments. instance move line of sight 0.4 mil, 0.1 mil scope must adjusted 4 clicks, while comparably 0.05 mil , 0.025 mil scope must adjusted 8 , 16 clicks respectively.

other

1.5/10 mil , 2/10 mil can found in short range sights, capped turrets, not used.

subtensions @ different distances

illustration of sight adjustment 0.1 milliradian increment.

subtension refers length between 2 points on target, , given in either centimeters, millimeters or inches. since mil angular measurement, subtension covered given angle (angular distance or angular diameter) increases viewing distance target. instance same angle of 0.1 mil subtend 1 cm @ 100 meters, 2 cm @ 200 meters, etc., or 0.36 inches @ 100 m, 0.72 inches @ 200 m, etc.

subtensions in mil based optics particularly useful target sizes , shooting distances in metric units. common scope adjustment increment in mil based rifle scopes 0.1 mil, called 1 centimeter clicks since 0.1 mil equals 1 cm @ 100 meters, 2 cm @ 200 meters, etc. similarly, adjustment click on scope 0.2 mil adjustment move point of bullet impact 2 cm @ 100 m , 4 cm @ 200 m, etc.

when using scope both mil adjustment , reticle mil markings (called mil/mil scope), shooter can spot own bullet impact , correct sight if needed. if shot miss, mil reticle can used ruler count number of mils shot off target. number of mils correct multiplied ten if scope has 0.1 mil adjustments. if instance shot 0.6 mil right of target, 6 clicks needed adjust sight. way there no need math, conversions, knowledge of target size or distance. true first focal plane scope @ magnifications, variable second focal plane must set given magnification (usually maximum magnification) mil scales correct.

when using scope mil adjustments, without mil markings in reticle (i.e. standard duplex cross-hair on hunting or benchrest scope), sight correction known target subtension , known range can calculated formula:

adjustment in mils

=


subtension in mm
range in m




{\displaystyle {\text{adjustment in mils}}={\frac {\text{subtension in mm}}{\text{range in m}}}}

for instance:

20 mm/50 m = 0.4 mils, or 4 clicks 1/10 mil adjustment scope.
50 mm/1000 m = 0.05 mils, or 1 click 0.05 mil adjustment scope.

in firearm optics, 0.1 mil per click common mil based adjustment value, common rule of thumb that:

one click changes impact many centimeters there hundreds of meters.

i.e 1 cm @ 100 meters, 2.25 cm @ 225 meters, 0.5 cm @ 50 meters, etc., see table below

adjustment range , base tilt

the horizontal , vertical adjustment range of firearm sight advertised manufacturer using mils. instance rifle scope may advertised having vertical adjustment range of 20 mils, means turning turret bullet impact can moved total of 20 meters @ 1000 meters (or 2 m @ 100 m, 4 m @ 200 m, 6 m @ 300 m etc.). horizontal , vertical adjustment ranges can different particular sight, instance scope may have 20 mils vertical , 10 mils horizontal adjustment. elevation differ between models, 10–11 mils common in hunting scopes, while scopes made long range shooting have adjustment range of 20–30 mils (70–100 moa).

sights can either mounted in neutral or tilted mounts. in neutral mount (also known flat base or non-tilted mount) sight point reasonably parallel barrel, , close 0 @ 100 meters (about 1 mil low depending on rifle , caliber). after zeroing @ 100 meters sight thereafter have adjusted upwards compensate bullet drop @ longer ranges, , therefore adjustment below 0 never used. means when using neutral mount half of scope s total elevation usable shooting @ longer ranges:

usable elevation in neutral mount

=


scope s total elevation
2




{\displaystyle {\text{usable elevation in neutral mount}}={\frac {\text{scope s total elevation}}{2}}}

in regular sport , hunting rifles (except in long range shooting), sights mounted in neutral mounts. done because optical quality of scope best in middle of adjustment range, , being able use half of adjustment range compensate bullet drop seldom problem @ short , medium range shooting.

however, in long range shooting tilted scope mounts common since important have enough vertical adjustment compensate bullet drop @ longer distances. purpose scope mounts sold varying degrees of tilt, common values are:

3 mils, equals 3 m @ 1000 m (or 0.3 m @ 100 m)
6 mils, equals 6 m @ 1000 m (or 0.6 m @ 100 m)
9 mils, equals 9 m @ 1000 m (or 0.9 m @ 100 m)

with tilted mount maximum usable scope elevation can found by:

maximum elevation tilted mount

=


scope s total elevation
2


+

base tilt



{\displaystyle {\text{maximum elevation tilted mount}}={\frac {\text{scope s total elevation}}{2}}+{\text{base tilt}}}

the adjustment range needed shoot @ distance vary firearm, caliber , load. example, .308 load , firearm combination, bullet may drop 13 mils @ 1000 meters (13 meters). able reach out, 1 either:

use scope 26 mils of adjustment in neutral mount, usable adjustment of 26 mils/2 = 13 mils
use scope 14 mils of adjustment , 6 mil tilted mount achieve maximum adjustment of 14 mils/2 + 6 = 13 mils