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Rifle Scope Glossary

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This information is taken from hand books which i was given by From the NRA when i first joined, as many of the guys on this site enjoy sniping, or even those who wish to get to know a little about scopes, this will just be a quick basic read.


Rifle Scopes Glossary Of Terms

Descriptions of rifle scopes can be a little confusing at times, especially if you're new to scopes and shooting.
Here are the basics;
What does 4x20 mean?
  • 4 - The first number means the magnification. In this example it is 4x (4 times) normal eyesight.
  • 20 - means the diameter of the viewing lens (not the eyepiece) in millimeters. (the tech term for this is "Objective lens size"
  • 4x20 - Therefore the scope is 4x magnification seen though a 20mm wide view lens.

And what about 3-9x40 then?
  • This means the scope has variable "zoom" capability.
  • In this case it ranges between 3 and 9x magnification though a 40mm wide view lens (objective lens)
  • Unless otherwise stated the numbers are Whole numbers, so on a 3-9x there will be a 3, 4, 5, 6, 7, 8 and 9x position
    but not fractions or some sort of granular 3.75x type of thing.
  • 3-9xx40 is the most popular general purpose scope size. If you can afford one get one.

Time for the more Tech stuff now

Exit pupil: The size of the column of light that leaves the eyepiece of a scope.

  • The larger the exit pupil, the brighter the image.
  • To determine the size, divide the objective lens diameter by the power ( a 4x40 model has an exit pupil of 10mm)

This is why big mag scopes tend to have big lenses e.g. 8x56 and why you dont get 3-9x20,
Because basically they would be rubbish.

Eye Relief
  • The distance a scope can be held away from the eye and still present the full field of view.
  • Unlike cartoons you don't have the eyepiece pressed up against your eye, if you did you are sure to get a black eye from recoil.

Field of View (F.O.V) : the side-to-side measurement of the circular viewing field or subject area.
  • It is defined by the width in feet or meters of the area visible at 100 yards or meters.
  • A wide field of view makes it easier to spot game and track moving targets.
  • Generally, the higher the magnification, the narrower the field of view.
  • Which is why variable magnification scopes are so handy. Spot the target at low mag and. Lock on and zoom in.

Windage & Elevation - The 2 turrets mid way down the scope body that are a key part of zeroing a scope.
When you fit a rifle scope they are up and to the right.
Windage - The one of the right
  • As the name suggest it is to do with wind
  • It adjusts the crosshair minutely left and right.
  • And for in the field adjustments for wind strength where, for example a high crosswind will make long range shoots veer slightly.
Elevation - The top one. Up and Down basically.
  • Again critical for getting zero and in the field where a strong head of tail wind effects a pellets lateral trajectory.
An experienced shooter will use the these turrets to make a situational zero adjustments. If you're not experienced don't worry. Just be aware and experiment as that's how you become experienced

  • A condition That occurs when the image of the target is not focused precisely on the reticule plane
  • Parallax is visible as an apparent movement between the reticule and the target when the shooter moves his head or, in extreme cases, as an out of focus image.
  • Some scores, higher priced ones typically, have parallax correction built in so that this focus problem does not occur.

That is it for this guide, will post more.
as i have just found pretty much all the documents that i was given from the NRA, even got a few army guides (Canadian army though) Which i will post on here at some point


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