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Air Guns How to mount a scope: Part 4

How to mount a scope: Part 4

by Tom Gaylord
Writing as B.B. Pelletier

Part 1
Part 2
Part 3

This report covers:

  • What optically centering DOES NOT mean
  • What optically centering really is
  • How to optically center a scope
  • Why do we do it?
  • Field target
  • Counting clicks — mechanical centering
  • Erector tube return spring
  • A better way
  • What about left and right?
  • Why so anal?
  • Pragmatic approach
  • Summary

Today we are going to discuss optically centering a scope. It’s going to be a difficult report for me to write, because the subject does not have much merit for airgunners. So I will compensate by adding some things that do have merit. Let’s go!

What optically centering DOES NOT mean

Let’s start with what optical centering DOESN’T mean. The optical center of the scope is not the place at which there are an equal number of clicks up and down and side to side. I say that and some of you already know it and yet the website “RifleOpticsWorld” has an online article written by “Rifle Optics Team” that says that setting a scope to the optical center is simply returning it to the factory setting. Excuse me????? 

Who in their right mind believes that a rifle scope comes from the factory set to its optical center? The factory assembles each scope as quickly as possible, checks it at certain points for quality and ships it. They don’t spend 45 minutes or more optically centering each scope they make!

This article then proceeds to tell the reader that optically centering is a solution to scope shift! No, it’s not! Optical centering has nothing to do with scope shift and it doesn’t fix it. I will tell you today what really does affect scope shift and how to correct it.

After reading this online article it is obvious to me that it was written by someone (or a team of someones) who was assigned to write it and they made stuff up as they went. If you understand what optically centering is, I invite you to read the article and see how far off the mark it is.

What optically centering really is

The optical center refers to the reticle and the field of view. An optically-centered scope shows zero reticle movement against a distant backdrop when the scope tube is rotated in a complete circle. Theoretically, it’s possible to achieve, but I’ve never seen it. The best I’ve seen is a reticle that moves about a quarter inch against a target 20 yards away when the scope tube is rotated in a complete circle.

How to optically center a scope

There are two ways to optically center a scope. The first way is to set the scope tube in Vee blocks and rotate the scope while watching the reticle against a distant target. I have done this with a quarter-inch dot as the target — set 20 yards from my position. Believe me — it can take a long time to get the scope pointing exactly at that dot — even with two people working at it! The easiest way I have found is to put a large white sheet of paper at 20 yards distance and talk a friend into drawing the dot, while you look through the scope that’s sitting in the Vee blocks and direct him. I initially thought the precision of the Vee blocks mattered, but I’ve since recognized that you can use a cardboard box with two Vee grooves cut in the right place to support the scope tube. It’s not the blocks that give the precision; it’s the fact that, other than rotating on its axis, the scope never moves..

Now, rotate the scope tube in the Vees and adjust the reticles until both lines remain centered on the dot. On a good day with some luck this takes about 45 minutes to get as close as you are going to get and the reticle will still move off the dot in a few places in its rotation, i.e. the intersection will move in and out of the dot as the scope rotates.

The second way to optically center the scope is to stand the objective lens on a mirror in a well-lit room or even outdoors in bright sunlight. Look down through the scope and what do you see? If the reticle appears blurry or doubled, adjust it until all you see is one sharp reticle. In other words, the real reticle is on top of its reflection. This way sounds easier than the first method because it is. But it doesn’t give results that are any better than the first method and maybe not as good. You see, the glass on the mirror is not parallel to the reflective surface on the back of the mirror, and you will always be off by some small amount.

mirror technique
With the scope’s objective resting on a mirror, adjust the horizontal and vertical reticles until the heavy reticles are covering the shadow lines — as best you can.

Why do we do it?

The belief is that once the scope is adjusted to its optical center it can then be mounted in an adjustable scope mount and, without changing the elevation or windage knobs, zero the scope at an ideal distance by adjusting the mount, only. You will have to use a scope mount that adjusts in both directions to do this. Having done this several times I can tell you that it is absolutely impossible to do. But, for the sake of argument, let’s assume it can be.

Once the scope is optically centered and also zeroed, you can then adjust the scope’s elevation reticle for range changes to your target. Because the scope is optically centered, the pellet will stay on the vertical reticle at all practical distances. Let me give an example.

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Field target

You have optically centered your scope and then zeroed it at 20 yards by adjusting the scope mount. You are shooting a .177-caliber pellet at 900 f.p.s. You will be on target from 20 yards to about 24 yards and then your pellet will start to rise above the center of the crosshairs. The pellet is not really rising, of course; it just appears that way to you.

From 24 yards to 28 yards the pellet rises until it is one pellet’s diameter above the center of the crosshairs but exactly in line with the vertical reticle. Starting at 29 yards until 32 yards the pellet will descend on the vertical reticle line but still be on the line, left and right. At 33 yards the pellet will start to descend below the center of the crosshair and by yard 35 it will be one pellet’s diameter below the center of the crosshairs.

dime and sight-in
This is the level of accuracy a field target competitor is seeking.

What you have just done is sight in an air rifle that is on target without any scope adjustment from 20 yards to 35 yards. You will be theoretically able to hold on the center of a kill zone on a field target within that range span and hit the paddle without touching the side of the kill zone — on all targets that have a 3/4-inch kill zone or larger.

All that I have just said is theory and it doesn’t work that way in the real world. In the real world the following is true.

1. It is impossible to optically center any scope. There will always be some slight movement of the reticle against a distant target as the scope is rotated through 360 degrees.

2. It is impossible to zero a scope with an adjustable scope mount. You can get close, but never exactly on.

Before we continue, let me define what I mean by exactly on. I mean the pellet is striking the point where the reticle lines intersect, with an equal amount of the pellet on either side of each line. This sounds anal, but the sport of field target makes shooters anal pretty quick. You see, there are kill zones that are smaller than 3/4-inches — some as small as 15 mm. When I competed in the late ’90s they were even smaller than that — down to 3/8-inch (9.44 mm). 

caliper and dime
This is the size (15 mm) of the smallest field target kill zone today.

If your pellet touches the side of the kill zone while passing through it can push the target “face” backwards hard enough to lock it upright, even though the paddle has been hit. The target won’t fall and you won’t get a point. This is the reason field target shooters are so concerned with accuracy.

Once when I was competing, one of the shooters brought his friend to the match to try it. He was a SWAT sniper and was confident he would do well. I think he thought he would teach us all a lesson in how to shoot. He finished in the middle of the pack of about 20 shooters and when it was over he told us that he was trained to shoot someone in the middle of their head. He reckoned that field target shooters would aim for one particular hair on the head — which is just about the case.

Counting clicks — mechanical centering

I hope I have made my point why optically centering a scope is impossible. Later on I’m going to tell you a very practical way to get the result that people desire from centering, but right now let’s discuss mechanical centering.

When you center a scope’s adjustments mechanically you are finding the spot in both adjustment where there are an equal number of clicks in all directions. If there are 123 clicks down there have to be 123 clicks up. Same for left and right, though they may not be the same number of clicks left and right as up and down. But don’t worry — it doesn’t matter, and here’s why.

Erector tube return spring

The reticle lives in the erector tube and the lines never appear to move when adjusted. That’s because they don’t. The entire tube moves while the lines remain stationary. Yes, there are European and Russian scopes whose reticle line actually do move, but they are an exception and not a part of this discussion.

There is a spring that’s mounted on a 45 degree angle to the erector tube and across from bothe adjustment knobs. It pushes back against both the vertical and right adjustments to keep the erector tube in whatever position the adjustments have put it. To the shooter it looks like nothing has moved.

At some point this spring gets relaxed and doesn’t push as hard. Then the tube can move without being adjusted — as in when it is jostled or bumped. That is when the scope starts to lose its zero and shifts randomly. So, centering the reticle (erector tube) mechanically doesn’t make much sense. Yes there may be 123 clicks on upward adjustment but the last 63 of them may be with the spring relaxed, so they are worthless. You don’t want to adjust the elevation there. Now that the scope is mechanically centered you have a lot of good downward adjustment that is useless (because you never adjust the scope that way) with very little upward adjustment before you start experiencing scope shift.

erector tube return spring
When the erector tube return spring relaxes, the erector tube starts moving on its own from vibration. Goobye zero!

A better way

Now I will tell you what really works and what top shooters around the world have discovered. Forget optical centering. Forget mechanical centering. Instead, adjust your scope until there is very little downward adjustment left. Once you zero the scope (with the adjustable scope mount) you will never use any downward adjustment. But you will use the upward adjustment, and this procedure has left a lot of it in the scope.

Everything I just said also applies to left and right adjustment, though it is not as critical. Gravity pulls pellets down; it doesn’t move them left and right.

What about left and right?

Okay, you understand how up and down works. What about left and right? Let’s assume that when you adjust the scope up the pellet stays glued to the vertical reticle. It never moves off the vertical line. It never does, but let’s pretend for a moment that it does. If you haven’t optically centered your scope, what happens when the farther out you shoot the farther the pellet strays to the left? 

Let’s also assume you are using a scope level for every shot, because none of this works if you aren’t. You notice that at 35 yards the pellet is half a diameter off to the left and at 45 yards it’s more than a full diameter off. What do you do?

What you do is check your zero at every 5-yard distance from 10 yards to 55 yards, because that is the distance at which you compete. Yes, I am aware the rules have changed and those distances are now stated in decimal fractions, but let’s keep this simple. And I said you check your zero every 5 yards and keep making small adjustments, but champions will then refine that to every yard — from 10 to 55 yards, or every meter from 10 to 50 meters.

What you do is adjust the left-right setting on your scope to get it as close to the centerline as possible at all distances. You never will get it perfect, but let’s say with careful work you get it to the place where your pellet is one diameter off to the left at 51 to 55 yards and one pellet diameter off to the right at 10 to 14 yards. It’s off by a lesser amount at the intermediate distances. Most field target competitors would be thrilled to have a scope that was that dialed-in.

Why so anal?

Do you really have to do any of this? Of course not. I don’t. You can go right on with your life, just as before. Nothing has changed. I wrote today’s report for those readers who were asking about optical centering. 

Pragmatic approach

The steps I have just given you (the last ones — the ones that really work) can take DAYS to complete! If you always want to see the bullseye get hit, watch a movie. This level of commitment to perfection is why some scopes cost more than $3,000 and some mounts cost over $500. You would be fooling yourself to think that serious competition can be done without a serious investment. Yes, you can follow these steps and do quite well on a budget, but remember — nobody races real cars in NASCAR.

My way is hard work. All the theory is out the window. As Jedi master Yoda told us, “Do, or do not. There is no try.”


In this article I have given you lots of things to do. But at their core there is one piece of invaluable advice. That is — it is impossible to do any of these things exactly. That applies to all of the procedures and desired results I have presented. You may think you are a perfectionist, but also recognize that for human beings there is no such thing.

You still should do your best to get as close as you can — so close that your hard work becomes a humorous anecdote that you can tell for many years to come, as I have just done for you!

author avatar
Tom Gaylord (B.B. Pelletier)
Tom Gaylord, also known as B.B. Pelletier, provides expert insights to airgunners all over the world on behalf of Pyramyd AIR. He has earned the title The Godfather of Airguns™ for his contributions to the industry, spending many years with AirForce Airguns and starting magazines dedicated to the sport such as Airgun Illustrated.

114 thoughts on “How to mount a scope: Part 4”

  1. It’s finally arrived!
    It has interchangable sights, which means you can took its fibre optic sights off and throw it into the garbage.
    Fibre optic sights makes me wanna puke.

      • Chris,
        Looks like u can change the barrel too. It’s powerplant can also be turned into a gas ram. I don’t think it’ll ever be an accurate rifle with all those modular features. I can visualize BB’s future report on this rifle. It’ll be a big surprise for me if this 34 turns out to be as accurate as it’s cousins.

    • Amen to that!

      I hate this fiberoptic stuff with a passion. Bonus points for putting fragile plastic at the front of the barrel where it’s exposed and you might want to grab it for cocking. The old-style front sights with a metal globe were just perfect as they were sturdy and you could grab them just fine. Those with interchageable inserts were even better as you could have any shape of front sight you wanted.

      Waffen Schlottmann here in Germany offers the Weihrauch HW45 and 75 (=Beeman P1 and P2) with a built-in 22mm rail. The 45 also comes with the traditional black sights:

      I don’t necessarily need the additional 22mm rail, but the iron sights alone might be reason enough to get that version. On my HW45, I painted the front sight black and removed the fiber insert in the rear sight. It works ok, too, but doesn’t look as nice.

      Give me wood and metal over plastic any time 🙂

      • RR,
        Did you ever try my suggestion of a fiber optic front sight with a peep? I have a few rifles set up that way and I really like it. Most of the time – lower light – it just shows up black anyway. If the light is right, instant red dot!

        • I have seen glowy thingy inserts for front globe sights.

          Have I tried this? No. None of mine have glowy thingy sights. To me that is a deal breaker.

          The whole thing about glowy thingy sights came from the powder burner world. They are great for quick shots in the guts, but are a hinderance for precise shooting such as the point halfway between the eye and the base of the ear.

          • RR & LMo,
            I’ve also found out this:
            I think synthetic stock is the way to go for this rifle; I’d feel in peace knowing that no wood was wasted for this rifle’s look. Its interchangeble plastic sights can never look nice with wood stock.

  2. With the field target group I compete with, 3/8 inch is the normal kill zone out to 20 yards. In the 50 yard NRA small bore targets I have, the 10 ring is 7/8 inch and the bullseye is 3/8 inch. This is shot with iron (aperature)!sights. Crazy!

  3. B.B.

    You keep mentioning “adjustable scope mount”. Please give an example of an adjustable scope mount that will work on magnum springers? While they may work fine on PCP’s I have found that they are garbage on springers….


    • Yogi,

      These used to come with a stop pin, but apparently no more.


      You will have to use one of these.


      A scope stop is not a bad idea anyway. I have had some stop pins on mounts that were small in diameter and ended up elongating the stop pin hole in the top of the compression tube.

      If you hunt around, you can find some really nice adjustable mounts, but they are going to end up costing more than your sproinger. Hardly worth it, most especially since the average “maximum accuracy range” for most magnum sproingers is 25 yards. Now if you take the time to really learn how to shoot a particular sproinger, you can stretch that out to 50 yards, but that takes serious devotion.

  4. BB,

    Thank you for taking the time to spell all of this out. This was a pretty involved (long) article. Some good reminders to stuff I have previously read.

    What happens when the scope is mounted off-axis to the bore (pointed left or right in relationship to the bore)? That is where shots will land left at near, on at zero and right at distance (or the reverse). That is where the adjustable mounts come into play once again.

    Short cut to that,… shoot at incremental yardages and either click (or) hold off accordingly based on actual shooting and the use of a cheat sheet.

    Again,…. well done on the article.


      • RidgeRunner,

        There is a possible solution IF the gun is worth it!
        I had PB that had the receiver rail mount holes drilled and tapped off axis to the treaded barrel port (argh! There is a name for that beside barrel port just can’t remember it at the moment!) So had a gunsmith bore out (next screw size up) the now moved on axis mount holes and tap them. It sounds silly to do all that when the next barrel might not have the same Bore axis…but it actually does since all these “problems” are stacking.


    • RR,

      Hmmmm?,…… it could work out quite well for you as long as she understands the concepts/parameters/adjustment methods and has the shooting skills. 🙂


  5. It has been confirmed.

    The 8th Annual North Carolina Airgun Show has been CANCELLED.


    Be sure to mark your calendars for the Friday and Saturday of the third week in October 2021.

    • RR,
      It’s for the good of all. Several people will have hold the rifles, placed their cheeks on the buttstocks, and etc… Every stock will have become a germ trap. Most hospitals have already reached their full capacity all over the country. Just take good care of yourself this fall, so you can enjoy many airgun shows in the future. Be safe, my man.

  6. BB,

    Great article, but I think there is more that can be said about the left-right impact of how we set up a scope on a gun. Unless we do something to address this issue, there really is nothing that “centering” the reticle will do, unless we are also adjusting laterally with adjustable mounts (which I do some of as well), but we can chase our tail on this end . . .

    The real driver of left-right issues is cant, and it is the cant that exists as a result of the not having the scope truly mounted over the center line of the barrel – no amount of chasing levels on the gun and scope independently will correct this misalignment. Fortunately there is a fairly easy way to overcome most of this – use a mirror when setting up the scope on the gun, and while mounting the scope look through the scope at a mirror that is set up perpendicular to the scope and gun at a distance, and make sure that the reticle is rotated to bisect BOTH the muzzle and the bell of the scope (don’t worry about level at all at this point), and only then do we lock it down. Once this is done, the scope will be centered over the barrel, and then when the scope reticle is leveled (this is when we use a plumb line to set up a level on the scope) the centerline of the scope will be over the centerline of the muzzle as a unit.

    Of course we can fine tune this will the adjustable scope mounts to remove any off axis conditions by centering our shots that way, but that is really fine tuning – the scope adjustments should suffice unless something is way off.

    Hope this helps someone.


    • Alan,

      “Once this is done, the scope will be centered over the barrel, and then when the scope reticle is leveled (this is when we use a plumb line to set up a level on the scope) the center line of the scope will be over the center line of the muzzle as a unit.”

      You had me up until this step. I see you are using the vertical line of the reticle to level the scope to the gun (instead of) messing with the horizontal line. (The scope is locked down at this point),.. so I fail to see the need for the plumb bob line step. Your going to do step #1, lock it down and then loosen it again for step #2?

      What did I miss?


      • Chris,

        Sorry I was not clear. You are correct that once we lock the scope down with the reticle bisecting the muzzle, we do not adjust it again. While we do not need to mount a level on the scope, it is a great idea for all the reasons BB talked about roughly a week ago – they help greatly with avoiding cant, especially when shooting on the bench (since we can easily check the level before a shot).

        So with this approach, once we have the gun and scope aligned, we add a level using the plumb line to level the “gun/scope system” by leveling the reticle to the plumb line, and then lock down the level on the scope without any change to the scope mounts to the gun – we never worry about “leveling the gun” because on it’s own that does nothing (in fact it can actually work against us).

        Once this is done, when we level the gun before shooting we have eliminated all cant and minimize any left/right sift induced by it.


        • Alan,

          Are you talking Benchrest?

          Known distance to target makes that practical.

          Also: “The real driver of left-right issues is cant, and it is the cant that exists as a result of the not having the scope truly mounted over the center line of the barrel ”

          You are talking Bore axis? Since barrels are seldom if ever truly bored centered.


          • Shootski,

            In a way, benchrest makes the criticality of this stuff less important, as we can just set things up for one distance and be very repeatable about it. While it can help there, in terms of making things more robust, it really helps when shooting at variable distances.

            You are correct that alignment of the optical axis with the bore axis is also very important, but these are typically not off by so much that lateral scope adjustment can’t handle it on its own – in most cases once we align the scope over the centerline of the muzzle, then we can zero laterally at our far distance and the shift as we come in closer will not be larger than any offset in the scope to the muzzle though triangulation along that plane – so minimal, but as BB says it can’t be perfect.

            If we have adjustable rings that can adjust for windage, and the alignment of the barrel and scope axis are far enough off each other, then it can help to make the adjustment via the mounts and then recenter the reticle to the muzzle in the mirror again. I only had one gun/scope combo where I had to resort to this second step.

            The ideal situation is to have the bore axis and the scope axis “perfectly” aligned in the same plane, and for that plane to be vertical to the ground when the scope reticle is level. That is why we try to make the scope and the gun barrel align vertically as a unit before we worry about leveling the scope/gun system.

            Hope that helps.

            • AlanMcD,

              I think much of what you do is similar to my approach. Both yours and mine are bedeviled by one unfortunate design fact in modern scopes the fact that the Erector Tube is hinged from one end. I know the amount of movement is small and has minimal angular effect at airgun typical ranges but the longer the range the more the effect for obvious reasons.


    • Also a great article! One of the reasons I attributed drift of the point of impact was the was the fact that the adjustment screws are bearing against a round erector tube, not a flat surface. As such, when adjusting elevation for example, it causes the windage screw to slide along the curve of the tube, resulting in an apparent shift in the windage POI. Over a short range of adjustment this may not be obvious, but a larger adjustment may show this effect, particularly the farther off the centerline the screw is. On the other hand, maybe it is the scope centering that is really causing this change…

      • Mr. Krill,

        First off — you are not related to the Krell, are you? I mean I don’t need to worry about the creature from the Id, do I? 😉

        You bring up a point that I have never considered. I will look into it, but my gut tells me that it’s been addressed.


        • BB,

          Not sure,… but I think you have mentioned that the windage can often move a bit when the elevation is adjusted (or visa-versa). Not sure if it was in comments or an actual blog though. Of course,.. there is a few variables,.. such as either being up/out too far, stiction and cheaper scopes.

          All in all,.. I think that it would be a good idea to mention it in an upcoming “how to mount a scope” blog. It is real. It does exist. New(bie) scope mounters need to be aware.


        • BB,

          Scope shift with regards to temperature extremes may be worth a mention too. I think you did an M-rod on New Years day one time in some extreme cold one time. As I recall, the AO scale was way off.

          The again,…. what is “cold” in Texas anyways?????,…. like 70 F,… or something? 😉


        • Forbidden Planet – great movie with Robbie the Robot! I have a 5″ plastic model of him on my desk along with B9. Did you know that the term, “blaster” as used in Star Wars was first used by Robbie in Forbidden Planet?

          Fred formerly of the DPRoNJ now Happily in GA

      • Krill,

        I am not sure it has been addressed previously, but the type of shift you are referring to does indeed happen. Not only over a large range of adjustment, but at longer ranges it becomes noticeable also. 1/4″ at 25 yards is 1″ at 100 yards and so on.

  7. BB ,

    Great article , I liked ” Remember , nobody races real cars in NASCAR ” Everyone looks at what someone does with a tricked out piece of gear , it is what you can do on demand with what you have !! Very interesting stuff . I bet the SWAT sniper was humbled a little . I don’t know how Tyler looks through that 40 power scope , You have to have such good body mechanics with that narrow Field of View . Gives me a headache thinking about it .

    Gene Salvino

        • 45Bravo

          I think a great deal is obviously good genetics and some luck but i truly believe good preventive maintenance works on human bodies just like lawn mowers, boats, guns and automobiles!
          Maybe even better since those mechanical things don’t have much/any ability to heal themselves.


          • Yes preventative maintenance on the body, and machines do work.

            But unfortunately no matter what we do, no one has YET beat the ride..

            My wife and I used to manage independent senior Living complexes, we have had many residents over 100, with widely varying physical and cognitive abilities at that advanced age.

            It’s not just physical preventative maintenance, it’s mental maintenance also.

            When I was young, I used to subscribe to the “live fast, die young, and leave a good looking corpse theory.”
            I lived fast, I was lucky enough to not die young, and now I am definitely not going to leave a good looking corpse…

            It’s been a good ride, and still hope to be around for a while longer..


            • 45Bravo,

              I will celebrate the 72 anniversary of my birth this coming January; God willing. I figured out years ago to stop Smoking (anything) and with the help of my son quit cold turkey when he was five. I cut out being a situational alcoholic and replaced it with responsible light social drinking. But the best thing i did was to start working with a Professional Trainer at 50 to ensure a balanced body and high order Functional Fitness. As far as mental health i consider that to be part of the body and it seems that having a high functioning body is a prerequisite for the platform to build good mental hygiene. I believe Ian, you have been in the situation with the I.L. facilities to note that grumbling about ones physical health is the biggest contributor to Senior’s poor mental hygiene; unless they have a diagnosed clinical mental condition. I really find it difficult to listen to the complaining of my peers when they can clearly do something in most instances to eliminate/mitigate the problem or at least keep it from getting worse. Few do more than misjudge my chronological age and just say they could do those things when they were my age. A rare few have chosen to at least ask how to do it too.
              I’m hopeful that i will have the best possible quality of life between now and moment(s) before i wink out, however soon that may be!
              I know much of that is in my control through the choices i make; just as it is true for most all of us.

              In good health be blessed,


              • That is so true..
                Your frame of mind has so much effect on your over all well being.

                Every time someone asks me how I am doing, my reply is

                I woke up today, so it’s a good day.

                Not everyone got that chance…


              • Shootski,

                “I’m hopeful that i will have the best possible quality of life between now and moment(s) before i wink out, however soon that may be!”

                Amen to that, that is truly what we all want.


    • Gene,
      shooting FT in the WFTF class allows unlimited magnification that is really helpful in ranging the distance to the target by using the adjustable objective. I actually shoot at 50x, because at 55 yards I want to be able to aim within the KillZone to compensate for wind drift. Lesser magnification makes that more difficult. I do sometimes quickly turn down the magnification to find the target, and then turn it back up after acquiring the KZ.

  8. I am not dedicated enough (read lazy) to go through all that. If when I finish putting a scope on an air rifle or firearm and I can get a few shots to gather together, I’m good. But if I were to get kinda serious about getting my shots closer together, this article is something I would start with. Oh and probably a higher end ($$$) scope.

  9. BB, thanks for tackling this involved topic on scopes. I’m learning quite a bit.

    Minor correction:
    Section: Erector tune return spring, 2nd paragraph.
    “across from bothe (both) adjustment knobs.”

  10. B.B.,
    Thanks for this report. Your “A better way” method is great. Now I understand why, in other reports, you use such a thick rear shim (credit card) on none adjustable mounts. That is to allow a greater usable upwards adjustment range. – Don

    • B.B,
      In rereading my post I should add that your “thick” shim seems larger than what is needed to zero the scope near the mechanical zero, even for a rifle with droop.
      I have seen that several scope manufacturers warn that a shim should not be used. In real life, how often is there a problem because of mounting a scope with a rear shim? – Don

      • Don,

        I have dented scope tubes with thick shims, but I still use those scopes. The best advice is to not tighten the scope caps too much. The scope won’t move when it isn’t in line with how the caps and scope bases were bored, so the caps don’t need to be tight.


        • B.B.
          Thanks, it sounds like this is a real issue. With the scope at an angle in the mounts the contact area is smaller so it make sense to apply less pressure from the caps. – Don

  11. BB, Great read, even if I need to do it three or four times. Not your writing, my lifelong battle with dyslexia. Is shooting uphill or downhill an issue? I can see how rotating the scope tube works, but I would expect to end up where started. I related to the third method you describe, and testing, at each range. The effect of wind, and all its variety, has to be the main issue. No pocket doppler with laser range finding yet? So all those hollywood snipers fiddling with their scope nobs before taking the shot are just acting? 😉
    .177 is a nice flat shooting example, and three or 4 pellet diameters variance between 20 and 37 yds means there can be allot of space between those mildots..
    Thank you,

      • Ah, more things to consider. So the point of adjustable rings, I can shoot close range, and for very long range, I adjust the rings for the general range, fine tune with the V and H controls on the scope? It may be within the existing range of adjustability on the scope, so, my fixed rings may be fine. On long range powder rifles,I have seen one piece rings with a radius cut on the top plate, and a matching radius bed on the bottom, with indicator marks, but they were shooting more than a thousand yards, to shoot at 150 yards is not possible?
        I dont think an airgun has the range for this feature.

    • Rob,

      Good snipers don’t just fiddle with the knobs.
      They know and compute a number of known external balistics variables and also worked really hard on reading the wind. They know how to read mirage in a scope to help with estimating the wind is that an effect you know about? What about the effect of shooting to the East or to the West or some angle to that. There are so many things beyond just the shooting up hill and down hill that others and I have posted about. Look up the rifleman’s rule of range estimation for up up or down hill. Then realize it isn’t really precise.

      Lots to know but i congratulate you on knowing that READING and then estimating the WIND IS the biggest issue! You are way ahead of the gadget types…other than wind flags and Telltale strings!


  12. It should be possible to make the mirror method more accurate. At first I thought of using the secondary mirror for a Newtonian type telescope. They’re available at reasonable prices even in the sizes needed (i.e. larger than the O.D. of the scope objective housing) they have a surface ground flat to a great degree of precision and the reflective coating is on the top surface – so the reflective surface and the surface the scope rests on are one and the same, removing any doubts about being parallel and any distortion caused by refraction that you get when looking through the layer of glass to the reflective surface in a household mirror. The problem with this is that there would be no way for light to get in to the scope from the objective lens end. Getting an optical window and putting it on top of the mirror would let light in (being precision ground you can get one with both surfaces parallel to each other to a very high degree of precision) which could be the best reasonably achievable level of accuracy you could get as a home user.

    Of course after all that I would have to adjust the scope with the elevation and windage dials to get the crosshairs where they need to be anyway – as I did after I’ve used the mirror method on my scopes – so the extra degree of precision may be of little practical value. In my case I only shoot at 10m and fortunately with my two scoped rifles only needed a few clicks to get the P.O.I. to be right on the crosshairs after centering.

      • I have a tendency to want to learn as much as I can about something and a tendency to try to make things “perfect” – and in the case of scope centering etc. I did just that. I drove myself crazy using v-blocks, then used the mirror method and fretted over the inaccuracy inherent in that. After all that was when I realized that with my shooting being at just one range (and most of it being with the aperture sights on the FWB or casual fun shooting) that I was really overthinking things for my purposes!

        “Close enough” usually ruffles my feathers at first but eventually I almost always make my peace with it.

        • Nowhere,

          “Close enough” usually ruffles my feathers at first but eventually I almost always make my peace with it.

          Ahhhh,…. a most humbling moment,……….. 😉

          Been there, done that. Like you though, I still fight it.


        • Nowhere,
          That tendency also applies to me. Sometimes being a perfectionist can be a curse, and it gets in the way of getting things done. I used to work with a friend building houses. He was always a “close enough” kind of guy. It drove me nuts because “close enough” was never good enough for me. He was very easy to work for though. He was good at roughing in but not very good at finish carpentry.

  13. Recenty, plenty of new break barrel springers have been introduced to the market, but still, nothing compares to an R9. In its class, it’s simply the best. That extra $100 – $150 is all worth it in my opinion. I sometimes see nightmares, where Weihrauch decides to replace its tunnel iron sights with fibre optic junk.

  14. B.B.,

    Thank you! I use both Aluminium Vee Blocks and/or a round 1/2″ Optical Plate Glass mirror to center my vertical crosshair or dot (non projected) and then check for how much actual depressed angle I can get. I use a photographic lens check sheet for astigmatic error or off axis lens system installation. Then i use a calibrated LASER boresighter to check for off bore axis base instalation or receiver drill and tap errors to correct what Chris USA was asking about a few posts up.

    Errata in 2nd paragraph of:

    Erector tube return spring

    “There is a spring that’s mounted on a 45 degree angle to the erector tube and across from bothe (both) adjustment knobs.”

    And after all that i agree with you it still will never be perfect. Even if the scopes temperature were never ever to change or some other thing throw all that hard work off…not to speak of the fact that spending that time learning to read the WIND is probably 1,000% more worthwhile.

    “When I am weaker than you, I ask you for freedom because that is according to your principles; when I am stronger than you, I take away your freedom because that is according to my principles.”
    Michael Malice


      • BB,
        I remember reading that back in time. 85 was an average rifle with an average price tag…
        But this 125 sniper in .25 cal seems to be quite the different breed. You probably don’t have time for this and that, so I fast forwarded the video to the 20 yrd shooting tests – it’ll take 30 seconds of your time tops.
        I’d love to see what this rifle is capable of in your hands. I remember you testing a .22 cal 125TH, and it was far from being impressive. Maybe the .25 cal is the secret ingredient for the 125 powerplant…

          • BB,
            I agree with you, ASP20 is a way better rifle than 125 sniper.
            You introduced me to ASP20. I have not had the pleasure of playing with one yet, but from what I’ve learned, it’s possibly the best gas ram break barrel around these days. It’s in a different league than 125 sniper and way better rifle than any hatsan springer hands down.
            I’ve always recommended my friends to buy good quality springers. The extra couple of hundreds you spend on a good quality springer is all worth it. ASP20 is a very good example of this philosophy; it’s only $50 more expensive than 125 sniper, and how much improvement that little difference on the price tag brings. It would probably the best 50 bucks a person could spend.

        • Fish
          I had a gas piston and spring piston .25 caliber and no good luck with them.

          They are just to violent. I did cut the spring down on the springer and the gun did smooth out a bit. But still never got the accuracy out of it that I wanted.

                    • Fish
                      Here read this again.

                      “I had a gas piston and spring piston .25 caliber and no good luck with them.

                      They are just to violent. I did cut the spring down on the springer and the gun did smooth out a bit. But still never got the accuracy out of it that I wanted.”

                      Now after reading that again. Here is what I mean.

                      I had 2 Hatsan .25 caliber guns. One was a gas piston break barrel and the other was a under lever springer.

                      I had no good luck with them. That’s another reason I’m not worried about the video.

            • Fish,

              Not bad at 20 yards (paper targets). That is what sells something to me,.. paper targets, 20-50 yards and center to center #’s.

              Those big springers can be a handful and way to hold sensitive. Also, while that one may have shot well, that don’t mean the next one will.

              If I was to get another springer,… it would (not) be an uber powered mega blaster.


                • Fish
                  Get you one and let us know what happens.

                  And I won’t even say told you so again till you show us some targets with it.

                  I’ll be waiting. And make sure you tell what its favorite pellet is. That would be good for others that are interested.

                  Over and out for now. Maybe. 🙂

                  • gf1,
                    not worth it to get upset. we just disagree on this matter. it’s that simple. and i don’t know why ur hatsans perform badly; rick eutsler has been doing a great job with ’em. 😉
                    i actually tried a friend’s qe 95 .22, and hated it’s sights. once i got used to the large front sight and the jiggly trigger, it was not that bad. maybe some airgunners are hatsan whisperers, who knows. 🙂
                    u don’t like kral either but see what rick does with a kral arms puncher armour .22,
                    these are good rifles despite ur bad experiences. i’ve never said, ‘go buy them,’ i just stated an opinion.
                    what i buy or don’t buy is totally my business. but i’ll say this much: if i were in the market for a breakbarrel springer, it would definately be an R9 .177. that’s a completely different matter. i’m sorry that u spent that much money on two poorly performing hatsans. i always tell people, with springers, u don’t have to break the bank to buy a good quality one. instead of buying 2 hatsans, i wish u had spent ur money on an hw80 or an hw90 – both have 25 cal options…

                    • Fish
                      Why do you think I’m upset?

                      I just tell the truth from my experiances.

                      Oh and you haven’t been on the blog as long as I have so how would you know what guns I have had.

                      Many is all I can say. So maybe from now on you should ask me if I had one before you reply.

                      Not try’n to be a snob. Just tell’n it how it is.

                      Maybe you need to expeeiance a few more. 😉

                      Hands down. That’s it.

                      Oh and by the way ihave had several Hatsan PCP’s andthey are good guns. Eveafew of the semi auto ones.

                      What i see with you is your a quick one to judge and your putting words in someones mouth that’s no way true.

                      Done with you.

                    • Read reply above.

                      Have a good one.

                      You are a young’n for sure no matter what your age.

                      Have fun learning life.

                      Wish you a good one.

                    • Fish,

                      Fish,… that is just GF1 being GF1. A bit pushy, insistent,… dare I say?,… “know it all”,………… but good, bad or otherwise,… he has had a ton of guns and has done a ton of modifications and pretty much knows his stuff.

                      He helped me a lot when I first came here.

                      Best way to approach GF1 on a topic is not to press it too far in getting into a debate.

                      Plus,… he shoots a (whole lot) and really likes to push the distance on whatever he is shooting.


                      (GF1,… do NOT go gettin’ a big head!) 😉

                    • Fish
                      Did you see your user name in any of my comments to Chris.

                      When I reply to someone I put their name at the begining of my reply.

                      And sorry bud but I reply to whoever I want when I want.

                      And since I made the rule of done with you I guess that means I can change it to whatever I want.

                      You know you are fun to play with though. By the way don’t you have something better to do than to reply to my comment.

                      And notice. I’m being very diplomatic here. 😉

                      And Fish. (and notice I said Fish) This is not your comment section. It belongs to BB’s blog. So sorry your out of luck with your request. 🙂

                      Oh and Fish my reply posted here because the thread is running out of room if you know what that means. Either way you will get my reply. 🙂

                    • Fish
                      If I remember right I never made no promise to you or anybody.

                      And if I did it doesn’t bother me in the least bit that I would break a promise to you.

                      But here is what I’m going to do.since your comments and mine here are useless.

                      I’m going to suggest to BB to strike our comments here that we have been making.

                      Basically its all trash. It needs to be omitted.

                      What a waiste of time.

                  • GF1,
                    Yup, I was just checking my RSS feed and saw your comment. Thanks for the reply, though my comment didn’t require any response. You may be right about the interpretation. When using text to communicate, it’s sometimes difficult to know one’s intent, even though we use emojis in an attempt to show sarcasm, or joking.
                    I respect your opinions because I know your are vastly more experienced with various airguns than I. It would be very foolish of me to argue on the subject. Hopefully, the flaming will stop now. You have a good day.

                    • Geo
                      You have a good day to.

                      And thank you for the respect. But you been around the block a time or two. Everyone has thier own knowledge and experiances to bring forward.

                      When I comment I comment on what I know. And I’m sure not going to dive in and start throwing responses at someone that I don’t know. Question them yes. And if they want to have a conversation and they want to debate a subject that is all fine.

                      But I would never start spouting off to someone and have no idea where they been or what they have done. How you talk to someone is what I’m talking about. And I wasn’t seeing that. Sorry but not putting up with anymore. Done with that stuff.

                      Turn the boat around the other direction and you will see what I mean. We can talk about something all day long but I’m not going to down you. Well of course that depends on how you are. Talk how you want to be talked to. If not well then see what happens.

                      Do you see what I mean?

                    • Geo,
                      You have a good day too…
                      All I did was sharing a link with BB and asking his opinion about Rick Eutsler’s center to center 20 yrd shooting experience with a .25 cal Hatsan 125 Sniper… No politics, no different languages – just airguns…
                      After watching the performance facts on this video, it would be foolish of me not to be tad bid impressed.

                    • BB,
                      125 sniper has been told to perform like that at 50 yrds on the first day of April every year. :^b
                      I replied to you with my opinion about ASP20 some where above. I love that rifle; needless to say, I love it more than any Hatsan springer. Once again, I have to mention how much joy that extra $50 delivers to an airgunner’s life.
                      I agree, ASP20 can do way better than 125 hands down. In the next ‘What do YOU want?’ report maybe we can ask for a .25 cal ASP20, what do you say?
                      Anyhow, all I said was how good a .25 cal 125 sniper had performed at 20 yrds in Rick’s hands; it shouldn’t have caused this much commotion. 🙂

              • Chris
                Don’t know if this will post in the right spot.
                But thanks for the words. I do appreciate it.

                And I know I know. The bighead. What can I say. Just try’n to say what I see when the time happens.

                Hope you been finding time to shoot.

                    • u two compliment each other under someone else’s comment pls. 🙂
                      i thought u were done with me, gf1; quit replying to my comment section.

                    • GF1 & Fish,
                      Gunfun, I agree with your comment above regarding the comments between you and Fish not being helpful. I have been reading and commenting in the blog since 2013 and it’s always been about airguns, crossbows, etc. I’ve always been impressed with the respect everyone has for each other, even though there are disagreements on occasion. There’s a lot of knowledge and experience here. We are a community helping each other and here to learn new things. Even though I am not really interested in pistols, I read the blog and comments every day regardless.
                      Sharing is caring. Can we just agree to disagree and move on? I, for one, am not entertained by people flaming each other. None of us knows everything, and everyone has something relevant to contribute. Let’s be respectful of each other.
                      Everyone have a great weekend. 🙂

                    • Geo
                      Hopefully your RS Feed is working because there was nowhere to reply to you so you see my reply to you.

                      What it kept remininding me of was when a political subject came up on the blog. Always ended up being a problem.

                      But what is in the back of my head is Fish might speak a different language and something was getting lost in the translation. (I think).

                      Anyway a big waste of time. From now on I’m going to just not talk to somebody when that issue keeps occuring. Maybe these conversations we just had will help people to stay away from commenting when someone in the future is showing that.

                      Whatever life goes on for now. On to the next ball game of life.

  15. BB,

    Are scope shift problems associated with insufficient erector tube return spring tension only a problem for some scopes, or is this a universal problem inherent to this type of scope, present at all quality levels?

    Why do they use a spring that will relax before it can supply enough force to stabilize the erector tube throughout its range of travel?

    Even if springs strong enough to supply that stabilizing tension limited erector tube travel at the other end of its range of adjustment, when the return spring is fully loaded, wouldn’t this be a better compromise in the end? It seems in either case you can only move the erector tube with in the main tube as much as the adjustment mechanism permits, but the use of a stronger spring would at least keep the erector tube stable at both extremes?

    If I have missed the point, why do you think achieving the spring tension to prevent erector tube instability has been so difficult?

    Airman of the Board

  16. I’m late to the blog today but I remember when you first wrote your articles on mounting and centering scopes. I can now confess that I tried for hours to optically center my scope via the V cutouts on a cardboard box. Never ever got there. Then I tried the mirror method which someone else swore by and stated it could be done in minutes. For some reason, my aged, fogged brain says this was an article from Dr. Beeman but I won’t bet money on that. I couldn’t see the reflected reticle images no matter what I did – bright lights, shining a flashlight at the mirror, using different mirrors, whatever. Never tried outdoors.

    What worked for me was getting the adjustment wheels mechanically centered and then, if I had to go more than 2.5 turns on the elevation wheel, I’d use a shim. For windage, I found reversing the scope mounts would do the trick. Today, I zero the scope at 50 yards for windage and I find I’m still able to put a pellet in the X ring at 20 without touching windage. Good enough for me!

    Fred formerly of the DPRoNJ now Happily in GA

  17. BB,
    Are the internals of a dot sight similar to a scope? In other words, could a similar problem happen with an over-adjusted dot sight as a telescopic sight?
    (I’m trying to decide if I should re-adjust what I presently have, or just go back to open sights)

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