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SIGHT SETTINGS - MOAs vs. POINTSBy Wayne McLerran |

Updated 9/28/13

In my book on Browning and Winchester BPCRs, I devoted a chapter to

sight adjustment and settings, and the impact of sight radius changes

due to different barrel lengths. Formulas were not provided but I

made a general comment that manufacturers design sights with

adjustment scales marked off in increments of a minute-of-angle

(MOA) or fractions thereof. I further explained that to be accurate

MOA adjustments are based on a rifle sight radius of approximately

34” (34.38” to be more exact). Hence there will be a “built-in” error

if the shooter installs the sights on a rifle with a different sight radius

and assumes the scale graduations represent MOAs. Although my

comments may be correct when referring to sight changes in MOAs,

the subject is somewhat confusing and another term, “points”, is

used by many shooters in an attempt to eliminate the confusion. But

some continue to refer to MOAs and “points” interchangeably,

resulting in continued confusion.

One shooter explained it this way. “Although a MOA is equal to

1.047” at 100 yards, most shooters equate one MOA with 1" at 100

yards and 2” at 200 yards and so on, which leads to an increase in

error as the shooting distance increases. Hence, the term "points"

came to mean 0.010", which is the vernier scale resolution of most

quality tang sights. We are a lot better at estimating distances on

the target in inches rather than MOAs. So, while we might say we

need a 2 minute (2 MOA) sight change, we really mean we need to

move the sight 2 "points" or 0.020". We should toss MOAs out of our

vocabulary because none of us are using it properly anyway.”

Recently I ran across a thread on one of the BPCR forums indicating

that rear sights setting are graduated for sight radii of 36” which, as

noted above, is correct based on the definition of a “point”. The

rather simple sight formula is: the ratio of sight adjustment (SA) to

sight radius (SR) is equal to the ratio of bullet impact change (BIC) to

target distance (TD). In other words, the algebraic formula is SA ÷ SR

= BIC ÷ TD. So let’s use the formula to verify the sight radius

necessary to make a bullet impact change of 1” at 100 yards using a

sight change of 1 point (0.010”). Rearranging the formula above to

SR = SA x TD ÷ BIC = (0.010” x 3600”) ÷ 1.0” = 36.0”. Hence, with a

sight radius of 36”, changing the rear sight 0.010” will move the

bullet impact point exactly 1” at 100 yards. But what happens when

the sights are used on rifles with different barrel lengths and the

sight settings are discussed without additional details on sight radius?

Shooters need to understand the differences and make the necessary

adjustments when attempting to utilize reported sight setting. For

example, shooter A has a rifle with a 38” sight radius. He provides

his sight radius, load data, velocity and reports a difference of 76

points from his rams setting to 1000 yards. Shooter B, a silhouette

shooter using the same bullet and getting similar velocities, reads the

report. He has a rifle with a 34” sight radius and wonders if his rear

sight staff has sufficient adjustment range to work out to 1000

yards. To make the necessary adjustment keep in mind that the

shorter the sight radius the less amount of sight adjustment is needed

to move the bullet impact point the same amount. Therefore the

difference in sight settings of 76 points must be multiplied by the

correct ratio of the difference in sight radii. In this example 76 x

(34” ÷ 38”) = 68 points. Thus shooter B’s rear sight staff must be tall

enough to adjust up at least 68 points (0.68”) above his ram sight

setting; being able to adjust up an additional 80 points (0.80”) would

be better and provide some margin.

In the above example “points” were used to clearly and accurately

describe the difference in sight settings along with the rifles sight

radius. If shooter A had reported a difference of 76 MOA the actual

amount might be interpreted as a change in sight setting of 0.76” or

0.726” or 0.796”, the latter two values determined by how the

correction factor of 1.047/MOA is applied. The exclusive use of

“points” eliminates any such confusion or ambiguity but the rifles

sight radius is still an important factor and must be understood when

discussing or conveying sight settings.

Wishing you great shooting,

Wayne

In my book on Browning and Winchester BPCRs, I devoted a chapter to

sight adjustment and settings, and the impact of sight radius changes

due to different barrel lengths. Formulas were not provided but I

made a general comment that manufacturers design sights with

adjustment scales marked off in increments of a minute-of-angle

(MOA) or fractions thereof. I further explained that to be accurate

MOA adjustments are based on a rifle sight radius of approximately

34” (34.38” to be more exact). Hence there will be a “built-in” error

if the shooter installs the sights on a rifle with a different sight radius

and assumes the scale graduations represent MOAs. Although my

comments may be correct when referring to sight changes in MOAs,

the subject is somewhat confusing and another term, “points”, is

used by many shooters in an attempt to eliminate the confusion. But

some continue to refer to MOAs and “points” interchangeably,

resulting in continued confusion.

One shooter explained it this way. “Although a MOA is equal to

1.047” at 100 yards, most shooters equate one MOA with 1" at 100

yards and 2” at 200 yards and so on, which leads to an increase in

error as the shooting distance increases. Hence, the term "points"

came to mean 0.010", which is the vernier scale resolution of most

quality tang sights. We are a lot better at estimating distances on

the target in inches rather than MOAs. So, while we might say we

need a 2 minute (2 MOA) sight change, we really mean we need to

move the sight 2 "points" or 0.020". We should toss MOAs out of our

vocabulary because none of us are using it properly anyway.”

Recently I ran across a thread on one of the BPCR forums indicating

that rear sights setting are graduated for sight radii of 36” which, as

noted above, is correct based on the definition of a “point”. The

rather simple sight formula is: the ratio of sight adjustment (SA) to

sight radius (SR) is equal to the ratio of bullet impact change (BIC) to

target distance (TD). In other words, the algebraic formula is SA ÷ SR

= BIC ÷ TD. So let’s use the formula to verify the sight radius

necessary to make a bullet impact change of 1” at 100 yards using a

sight change of 1 point (0.010”). Rearranging the formula above to

SR = SA x TD ÷ BIC = (0.010” x 3600”) ÷ 1.0” = 36.0”. Hence, with a

sight radius of 36”, changing the rear sight 0.010” will move the

bullet impact point exactly 1” at 100 yards. But what happens when

the sights are used on rifles with different barrel lengths and the

sight settings are discussed without additional details on sight radius?

Shooters need to understand the differences and make the necessary

adjustments when attempting to utilize reported sight setting. For

example, shooter A has a rifle with a 38” sight radius. He provides

his sight radius, load data, velocity and reports a difference of 76

points from his rams setting to 1000 yards. Shooter B, a silhouette

shooter using the same bullet and getting similar velocities, reads the

report. He has a rifle with a 34” sight radius and wonders if his rear

sight staff has sufficient adjustment range to work out to 1000

yards. To make the necessary adjustment keep in mind that the

shorter the sight radius the less amount of sight adjustment is needed

to move the bullet impact point the same amount. Therefore the

difference in sight settings of 76 points must be multiplied by the

correct ratio of the difference in sight radii. In this example 76 x

(34” ÷ 38”) = 68 points. Thus shooter B’s rear sight staff must be tall

enough to adjust up at least 68 points (0.68”) above his ram sight

setting; being able to adjust up an additional 80 points (0.80”) would

be better and provide some margin.

In the above example “points” were used to clearly and accurately

describe the difference in sight settings along with the rifles sight

radius. If shooter A had reported a difference of 76 MOA the actual

amount might be interpreted as a change in sight setting of 0.76” or

0.726” or 0.796”, the latter two values determined by how the

correction factor of 1.047/MOA is applied. The exclusive use of

“points” eliminates any such confusion or ambiguity but the rifles

sight radius is still an important factor and must be understood when

discussing or conveying sight settings.

Wishing you great shooting,

Wayne