Minute of Angle

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Obviously, at times you will need to alter where you bullet hits the target, to allow for changes in wind, or proximity to the target.

Wind can move a bullet in flight significantly, and distance from a target will alter the trajectory, and as such the point of impact.

To work out how much you need to adjust you sight settings you need to know how much a minute of angle - (which is used on scopes and sights) will move a bullet at a certain distance.

You can do this by using some simple trigonometry.

Minutes of Angle

 

100 yards = 3600 inches.

1 minute = 1/60th of a degree

To work out the distance x

Tanθ = opposite/adjacent

In this case:

Tan 1’ = x/3600

As 1’ = 1/60 degrees

Tan (1/60) =   x/3600

which rearranges as  x = 3600 Tan(1/60)

Tan (1/60) = 2.9 x10-4

So x = 3600 [2.9 x10-4]

Therefore x= 1.047 “

1 Minute of angle at 100 yards = 1.047 inches.

At 900 yards it is 9.423 inches etc.

This can easily be rounded down to 1 inch at 100 yards.

1 minute of angle moved on the scope will move the bullet 1 inch for every 100 yards of target distance.

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NRA targets are scaled so that as the distance increases the size of the target also increases; the bull ring therefore is set at a diameter scaled to 2 minutes of angle.

However, you must remember that the bullet's trajectory will not follow a straight path, but will drop the further it travels due to the combined effects of gravity and air resistance.

 

Bullet drop

To allow for this you must bring your scope/sights onto target – (see 'Approximate Windage Allowance and Elevation' slide show in Multimedia), then smaller adjustments will be equally scaled for all NRA targets (e.g. 1 MOA at 600 yards will have the same effect on bullet placement on the target  as at 1000 yards).

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