What’s wrong with scope adjustments?

by B.B. Pelletier

This question came in from Pestbgone, who asked why a scope with 1/4″ adjustments at 100 yards did not respond with 10 times the number of clicks at 10 yards. In other words, why don’t 10 clicks move the pellet a 1/4″ at 10 yards, if one click moves it 1/4″ at 100 yards. Great question. Simple answer.

Nothing is for certain
How do you think scope makers get the reticle to move 1/4″ at 100 yards? They do it by using a screw with a very fine thread. This screw moves the erector tube by a small amount. Attached to the screw is a ratchet or click detent that produces an audible and tactile signal that one “increment” of distance has been covered. For example, one click equals 1/4″ at 100 yards.

The truth is that one click never does equal 1/4″ at 100 yards. It’s close, but not exact. That’s because screw threads are not cut that way. While it’s possible to get close, it’s next to impossible to get exact movements that equal the measurements scope manufacturers put on the adjustment knobs.

Does that bother you? And, why do I know all this? Well, about 10 years ago, several field target shooters came up with a brilliant idea. They reasoned that if software programs could calculate pellet drop, they would never need to sight-in their guns at more than one distance. They could simply adjust their scopes for all other distances once they had been “sighted-in.”

Surprise, surprise!
Only, it didn’t work that way. When they actually tested their theory, they discovered that click adjustments came in all sizes. They found scopes with 1/7″ adjustments, 1/5″ adjustments and many others. What they never found were scopes with adjustments that were identical to the inch value given on the adjustment knobs or in the scope’s instructions.

You would think that this would cause a tremendous uproar, but it never did. In fact, very few people today even know about this phenomenon. The truth is that when someone goes to the range, they adjust their scope til the gun hits where they want it to, and they pay little attention to the actual click value.

Airgunners, however, have a greater need than firearms shooters to know the click values. Because our adjustments are all at much shorter ranges, we have to apply many more clicks to move the strike of the pellet. Therefore, we notice when things don’t seem to be working out the way we think they should. That’s why Pestbgone noticed that his scope was not adjusting as expected.

Do the work
There’s not substitute for actually sighting-in a scope at all ranges you wish to shoot. That’s what the experts do, and that’s what you’ll have to do if you expect to hit what you’re shooting at. This is the reason that my explanation of the two points of intersection (where the pellet is right on the crosshairs) is so important. No one has time to sight-in at every possible distance they will shoot. You need to find a good medium range to sight-in, then test your rifle at different distance throughout your intended range of use. Don’t count on click values being correct. Even on precision target scopes, they’re going to be off a little.

21 thoughts on “What’s wrong with scope adjustments?

  1. B.B.,
    Thanks for the explanation and placing the responsibility back on me, the shooter, to do the work of knowing my equipment. I guess I’m used to one crank of the handle being exactly .100 or one turn of the thimble always being .025. So when changes or adjustments don’t fall into the pattern that I’ve already set up in my head, I assume there is something wrong. The whole process of airgun shooting seems more like a mixture of science and art. The science of the precision equipment and precise measurements, and the art of dealing with the variability of the equipment and conditions and ourselves, to end up with a precise and predictable result. And all this from a system that is often unpredictable.
    Certainly keeps it from getting dull !
    Thanks again,
    Pestbgone


  2. BB,

    mildot reticles are very popular nowadays. How precise are they, assuming the magnification is always the same?

    Markus


  3. Hey BB

    While talking about scopes, I noticed that my leapers 3-9X50 will fog up frequently when I take my gun from the basement to my backyard. Lately it has been very humid so I guess it is expected. I thought that leapers coated there lenses with that emerald coating which I thought I had read that would keep the scope fog proof.
    Should this happen with the coatings? Are there any coatings that one could apply themselves to the lenses to keep the fog out?

    Thanks, Kyle.


  4. Markus,

    Mil dots are optical measurements rather than machine screw threads, so they are many times more exact. An optical plant that can grind lenses to exact formulas can also apply mil dots just as precisely.

    In other words, you can trust the scope manufacturer.

    B.B.


  5. Kyle,

    Your scope is filled with nitrogen so it isn’t supposed to do that. When the temperature changes radically, they may fog internally for a brief time. If the fog is on the outside, you must blame nature, as nothing can be done about it. Don’t use the bathroom anti-fog spray without consulting the manufacturer, as it may attack the lens coating.

    If the fog is internal and lasts more than a minute, you should contact Leapers or the dealer who sold it and ask what can be done. These are supposed to be fog-proof optics.

    B.B.


  6. Hey BB

    Thanks for the help. The fog is on the outside and can be wiped away with a cloth. I was just unsure whether my scope had problems or if it was just the 90% humidity here. I guess natures to blame here.

    Thanks again, Kyle.


  7. Greetings B.B. and fellow airgunners!

    I have a question regarding underlevers and side levers. Question: do the levers have a bit of play before the spring begins to compress, thus opening the sliding compression chamber? Or is that sliding tube only opened under pressure?

    Just part of my research before I purchase…Although this question may be moot since my mouse cursor seems to like the Beeman R1 BUY BUTTON..a LOT. TIA folks.

    -Paul


  8. i know pyramyd air doesn’t sell the QB-78 rifles, but I was wondering if you had any experience with them. I plan to buy one that fills from a 9oz co2 tank and I wondered if they are accurate/quality. They copy the Crosman 160 and even though i don’t like buying Chinese, I’d like to buy a copy of a legendary rifle. I’ve heard only good things.
    thanks,
    hb

    PS
    thanks for the heads up on the taurus .45, i was planning on getting one!


  9. BB,

    Thank you for helping to make us all feel less crazy.

    I remember my dad bought me an Omega wristwatch as a high school graduaton present. It was guaranteed to lose or gain not more than 1/2 second a month. I used to cradle it and think, ‘at last; something in my life that can be depended on!’ Only later did I read the fine print that said ‘can be ADJUSTED not to gain or lose more than 1/2 second a month.’

    Things such as your blog help us all feel less nuts. Thanks!

    -Joe


  10. B.B.,

    I just got cough up on my reading.

    Are .177s more accurate than .22s?

    If both guns and pellet had the same tolerances. It seams like mass,velocity,size,coeficent and stabilization would all play a role.

    I looked at my Shadow today and there are two holes under the metal scope stop. The one in front is threaded and the one behind it is larger and not threaded. It’s slightly larger than my B-Square pin stop.

    The strange thing about it is that both appear to go completely through the receiver. I believe that I can see the rear guide.

    I know you have said in the past that manufactures change there guns and have many different scope mount specifications. It blew my mind when you described the trouble that B-Square went through to produce a mount that would fit most guns.

    Now this about scope adjustments. BTW are most field target shooters clickers?

    Some great reading , keep up the good work!!!




  11. CyberSkin,

    All WINNING FT shooters use click adjustments. I tried it both ways, and when I switched from holdover to click adjustments, I added about five points to my score.

    B.B.



  12. CrimsonSky,

    With most underlevers, it’s difficult to load before cocking. I can do it, but each gun takes a different technique. For example, with the CF-X, you have to pull the lever down a little to take tension off the rotary breech, which can then be opened to load the gun.

    B.B.


  13. Thanks for the answer B.B., I had wondered for some time if it were possible to load them prior to cocking. They are all such different animals, but the same species apparently. Have a great weekend!

    -Paul


  14. On another note, you were right on with the Leapers Mill dot illuminated 4-16×50. It arrived from Pyramid yesterday, and simply amazing optics for the price!

    cheers
    Paul


  15. HELLO B.B.

    I HAVE A BUSHNELL SPORTVIEW 3-7X20MM
    SCOPE AND I’M PLANNING ON BUYING THE GAMO HUNTER 440 AND WAS WOUNDERING IF THIS SCOPE CAN BE USED ON A SPRING PISTON AIR RIFLE LIKE THIS ONE

    THANK YOU


  16. Your scope was made for a .22 rimfire and may not be able to withstand the recoil of spring-piston rifle. I can’t say that for certain, as I don’t test scopes like this, but most scopes with a small tube aren’t made for heavy-recoiling air rifles.

    B.B.


  17. I have bought several scopes, the latest being the leapers 3-12×44 30mm tube illumniated. For some reason on this scope it is very difficult to change magnification-almost to the point where it takes two hands. Is there some type of adjustment that I don’t konw about or is this just one of those things i am going to have to suffer with-thanks, Scott


  18. Scott,

    These adjustments on all scopes are made at the factory, and they tend to lean towards to the stiff side. That’s because they do break in over time and become easier. But you don’t want them to be too easy, or things will change without you wanting them to.

    Grease is the major reason the adjustment is hard. It’s thick and viscous, but there is very little on the threads. A properly adjusted scope will last a long time.

    B.B.


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