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Scoping problematic airguns

by Tom Gaylord
Writing as B.B. Pelletier

This report covers:

  • The problems
  • Problem 1 — All rifles are droopers!
  • Problem 2 — horizontal alignment
  • Problem 3 — scope eyepiece is in the wrong place
  • What is the solution?
  • Clearance
  • Summary

Today’s report was partly inspired by reader Decksniper, who asked this about the Seneca Aspen rifle:

“I am interested in the shim you used to mount the Bugbuster on the too narrow dovetail. A closeup picture would be helpful.”

I told him I would photograph the shim in the next part about the Aspen, and I will, but this morning (yesterday for you) I was faced with scoping another rifle — the Diana Stormrider Generation II PCP, and it suddenly dawned on me that scoping airguns is one of the biggest challenges I face in writing this blog. As I pondered that it occurred to me that scoping guns is a challenge for all of us. Some may not have realized what a challenge it is because they have become adept in avoiding the problem altogether, but a challenge it is.

Heck — it’s a challenge to scope a firearm, too. That’s why people pay gun shops to boresight their rifles for them. When they get out to the range I see that they haven’t got the foggiest notion of what to do next. That always happens on the 100-yard firing line, where they will staple a cardboard pie plate to the backer board and sit at the shooting bench for an hour in frustration, wondering where their bullets are going. At least airgunners can start out at a closer distance, so they have a little better chance of connecting with paper!

By the way, these firearm shooters often show up at the range with a fresh box of 20 cartridges, expecting to get zeroed in 4-5 shots. Ha!

The problems

Today I want to talk about the problems of scoping an airgun for the first time and tell you some of the things I do to address them.

Problem 1 — All rifles are droopers!

My first assumption is that all rifles are droopers. Their barrels point down in relation to the scope base on their receivers, which means they will invariably shoot low. Is that true all the time? No, it’s not. But the number of guns (airguns and firearms) that DON’T droop is minuscule compared to the ones that do — at least in my experience. People sometimes ask me what if they correct a gun for droop when it has none. Is that a problem?

Most of the time it’s not. You just end up with more vertical adjustment. There is no problem adjusting the scope on a normal rifle down below the midpoint of the elevation range. You can take it all the way down to where the adjustments stop and the scope will perform as it should. Unless the barrel is bent up and the rifle shoots too high, this will not be a problem.

It’s when you adjust above the midpoint of the vertical range that problems start to occur. At some point in the upper range of vertical adjustment the erector tube inside the scope where the reticle lives will loose all spring tension and start to “float.” At that point the reticle will start moving with the vibration of each shot. You will see that as scope shift. You won’t be able to hold a solid aim point.

I’m not going to discuss all the methods of correcting this problem, but I will name them.

1. Shim the scope.
2. Use an adjustable scope mount or base.
3. Use rings or a scope base that has droop compensation built in.

Problem 2 — horizontal alignment

I’m talking left and right now. You sight in at 10 feet and your pellet strikes the paper 6 inches to the right of your aim point. If you back up to 10 meters without correcting it the next pellet is going into the wall!

When it’s bad like this you can always see the cause. Hold the rifle so you look down on the scope and compare its line to the line of the barrel. It will be noticeably off or angled. The reasons for that are varied.

1. The scope rings are not correctly mounted on the scope base. Look closely at the pointed jaws of the scope rings and make sure that are in the grooves where they are supposed to be. If you have two piece rings, one will often be mounted correctly and the other one will be out of the grooves on one or both sides.

2. You are using cheap rings that are not bored straight. This doesn’t happen with quality rings, but with cheaper rings it’s common. The angle will be harder to see when this is the problem, which is why bargain scope rings are never a bargain. With two piece rings you can sometimes fix the problem by turning one or both rings around, or by swapping them, front and rear — or a combination of both things.

3. The grooves on the rifle are not cut straight with relation to the barrel. This is not common.

4. The barrel is offset. This happens on PCPs that have free-floating barrels. There is usually a barrel hanger with two or thee small screws that can be loosened so the barrel can be pressed back into alignment with the scope and receiver.

Problem 3 — scope eyepiece is in the wrong place

The eyepiece is positioned incorrectly so your eye does not see the full image in the scope. This is very common with compact scopes and with one piece rings. Both force you to mount the scope someplace on the rifle that may not correspond with where you need it to be. The solution is not simple, but here it is.

1. Take the scope you intend using and see how far from your eye the eyepiece needs to be for the image to be full. Usually there will be a short range of distance. Once you find it, find a scope mount that allows you to position the scope there.

Woah! That’s a lot of you in the solution, isn’t it? There must be an easier way.

Many new people ask the salesperson to recommend a scope and mount that will be right for the rifle they are buying. There’s just one huge problem with that. The shooter is also a factor in the scope mounting equation and, unless that is taken into account, they are just guessing. Some things to consider:

1. How long is your neck?
2. How broad are your shoulders?
3. At what angle do you hold a rifle, relative to your body and the intended target?
4. How consistent is your cheek weld?
5. What is the shape of your face?

Selecting a scope and mounts for a rifle without seeing both beforehand is like buying a car, sight unseen. No, it’s worse than that, because cars are purposely made for a broad range of drivers. Buying a scope and mounts without seeing both together with the rifle is like getting glasses without having an eye examination.

What is the solution?

I have just told you that it is nearly impossible to get a scope and mount without seeing them in person. Is there any hope? Yes, there is. Here are some things that will help you a lot.

1. Use two piece rings. These give you a broader degree of latitude as to where the scope eyepiece can be.

2. Get a scope with a long eye relief. Eye relief is a measure of how far your eye needs to be from the eyepiece to see the whole image in the scope. Some powerful scopes have a very short eye relief and demand that your eye be in the exact spot or the image will appear black. This isn’t always bad, because it helps you position your eye in the same place evey time, which minimizes parallax errors. But it’s not as flexible.

Lower powered scopes usually have a very long eye relief and are very easy to use. The down side is they have a larger parallax error. That may not matter if you don’t care about the last bit of accuracy.


Getting the scope to clear the parts of a rifle is another concern. This is where a salesperson should be able to help. There are a couple things to watch.

1. Does the objective bell clear the rear sight or barrel or barrel band? The rear sight is the biggest issue. A scope with a large objective bell that’s mounted in lower rings may not clear the rear sight and even the barrel.

2. Does the objective bell clear the breech of a breakbarrel when the rifle is cocked? Long scopes are at issue here and this is something that is difficult to determine without having both the scope and gun in hand. Sometimes the scope can be moved back a little, if the eye relief will permit it.


Those are the main things that I face every time I scope an airgun. Are there others? Sure. Things like:

1. Is the scope clear enough and powerful enough for the kind of shooting intended?
2. Are the rings the right diameter for the scope tube?
3. Is the base of the rings compatible with the scope base on the rifle?
4. Are the reticle lines appropriate for the kind of shooting I intend doing?
5. Do my scope mounts have the right scope stop for the gun I’m mounting them on?

Scoping an air rifle is a challenge for me because I test so many different air rifles. It’s a challenge for you because you don’t have that many scopes and mounts to pick and choose from.

All of us want a well-mounted scope. It’s so much easier to shoot when the scope is mounted correctly. I have had to learn to adapt to guns whose scopes may be less than optimum. I hope you don’t have to do the same.

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.

48 thoughts on “Scoping problematic airguns”

  1. SIghting in and using a scope certainly is a lot more complicated than on TV!

    You haven’t even gotten into scope cant and parallax yet. It really does make you appreciate the beauty of ghost ring sights, red dots, and holographic sights.

  2. B.B.,

    Most excellent!!!! Having spares around is handy. Since most of us are buying sight un-seen,… expect to re-buy some stuff. Eventually, you will have multiple height rings that come with a scope. Have enough and you can play with the height.

    No bull,… I had the M-rod first. Then got on line and found all of the scope dimensions as well the ring dimensions. Then,… I did a full scale drawing. I knew eye relief from other rifles, so that gave me the butt to ocular distance (or at least a pretty good guess). In the end, the objective was 1/8″ off the shroud. On the drawing it was 3/16″,…. so near a perfect “prediction”.

    The TX200 and LGU had shallow 11mm grooves. The M-rod and Maximus are deeper cut and taller and (way) better. The Red Wolf is very good as well. I have been lucky to never get any that were too narrow.

    Yes Sir, it can be quite the challenge, but gets easier with experience.

    Good Day to one and all,….. Chris

    • Chris,

      I do the same thing – get all the dimensions and do a full scale mock-up to check for clearances and fit.

      Saves a lot of frustration and $$$ doing it that way.


  3. B.B.

    I got into a discussion on one of the forums where the poster wanted to mount a LARGE 56mm objective scope with a 34mm tube onto a 6 lbs rifle. Maybe you can explain better than I can why this is not a good idea?


    • Yogi,

      I can but I won’t. I have learned over the years that if someone wants something you have to let them have it their way. They will then discover many of the things you wanted to tell them.

      If you tell them now they will listen, but it won’t affect their decision. People want what people want.


  4. An excellent blog B.B.!!

    Most people are much too casual in buying a scope and rings set only to find out later that they have problems to correct.

    The five points you mention in the “Problem 3 — scope eyepiece is in the wrong place” section are things that can be compensated for with a stock that fits correctly. A good fit encourages a consistent hold and improves accuracy.

    I talk about this in my next guest blog where I hope to encourage people to make their own stock as a learning experience. Attached is a picture of a partially complete “reference stock” used for fitting. The upper image shows the stock being configured and the lower image the stock ready for shooting.


    • Hank, I will be very interested in your blog, and I suspect I am not alone. I have done a bit of wood work but limited to repairs. I am intrigued on the whole process, from blank selection to finish.

    • Hank,

      Like others,.. I am looking forwards to your blog as well. Please give some attention to the type of power tools required,….. stationary and/or hand held. What may seem like everyday stuff to you, might seem exotic to the rest of us. I am familiar with wood working tools and process,… but do not consider myself to be a fine woodworker by any stretch. For example,.. I would think a table saw, drill press, planer, sander and band saw would be the basics. All stationary. Then,… hand finishing tools powered by hand/electric/air.

      Your “Try Gun” is very interesting.


      • Chris,

        The only power tool required to make the Try Gun stock that I will be detailing in my blog is a table saw (I have a 10″ Dewalt contractor saw). A drill press is handy but not necessary. A good sharp rasp is something that is really useful for shaping stocks.

        I’m no “cabinet maker” either, I just like to putter around 🙂 You don’t need expensive tools or materials to make your own stock. I just came in from cutting some pieces of cherry and maple that I filched out of the firewood pile to make a “camo-pattern” stock for the Maximus. I asked Dad to help me put the little pieces together as he is very good at doing puzzles. LOL!


  5. BB

    Wow, this is the first time a question from me has triggered a report. I feel honored somehow.

    The shim photo is coming so there is more on this subject to look forward to. Readers who are new to mounting scopes may think this is some kind of dark side to stay away from. On the contrary, the opposite is true. I get as much fun switching scopes, other optics and apertures as I do shooting. Having many choices on hand helps overcome the issues mentioned. I have extra droop compensators, dovetail/Picatinny adaptors and vice versa, medium and high mounts and both 1 inch and 30 mm rings. Also helps to have extra scope stop screws and narrow to wide dovetail converters. I have had good luck with popular priced mounts and rings so far. I usually prefer high mounts for reasons you mention plus it is easier to load pellets on many guns. My neck and body shape has no problem with high mounts.

    Have a good day everyone and keep your spirits high.


    • Hey Deck,

      Do you have any suggestions for leveling the cross-hairs??

      I’ve tried all kinds of things using levels and stuff and (with much mumbling and muttering under my breath) have come to the conclusion that is is me that is out of kilter 🙂


      • Hank

        Hope I understand your question. I don’t hunt with airguns and I shoot paper targets only. They consist of certain types of cardboard boxes that I cut in square or rectangles. I either tape target bulls or stencil draw bulls directly on the cardboard mounted on a heavy gage steel target holder. Reticle alignment is simple. I parallel the scope reticle with either the top or bottom of the rectangular target. I’m always square to the target and have no need for a scope level. I don’t care if the target is slightly canted or not. You can do the same thing with targets that have perpendicular lines.


        • Deck,

          I always try to get it perfect too. But,… if the rifle is canted a bit and the scope appears level to the target,… and IFFFFFF,…. the shooter (repeats) that every time,… won’t the results repeat? I am not sure. I am just tossing it out there. From what I understand,…. cant one shot and level the next shot is not good. Level all shots,.. cant all shots,… gets the same results?

          For me,.. I use a string with a weight (plumb bob) for set up. I also check with levels if I can. I also repeat, rest and repeat. The way I figure it,…. a weighted string is not going to lie. Doing that and leveling a target and the probability of error is pretty slim.


          • Chris

            The rifle doesn’t care about being level or canted in my opinion as long as it is in the exact same place every shot. BB may want to weigh in on this but think he has said as much. The plumb bob string is an excellent way to get consistency and works well also when targets are ferel sodas or even pests if they stay still long enough.

            Thinking you could teach me a trick or two.


            • Deck,

              Not sure about the teaching part. I am here to learn just as you are. If there is one thing I have learned,…. it is “ideal” if (everything) is repeated for every shot. Vary from that and things will be less than ideal to whatever degree. Cans, pests, paper targets,… whatever it may be.


            • Deck,

              You nailed it. Artillery pieces shoot miles without even seeing their targets. But they have to see the aiming post the same way every time. It’s probably done with computers these days, but that is what the computer is doing, plus the work of the fire direction center.

              I have seen 10 meter rifle champions cant their rifles noticeably — the same way every time.


                  • B.B.,
                    I meant to spell canting. Much has been written about how the rounds path is an arc that crosses the point of aim (when sighted in), at one or two points. When the gun is canted, the round crosses the plain of aim away from the center line at the farther sighting point center. I hope you get my meaning.

                    • Gerald,

                      What the pellets do downrange is describe a sideways arc on the target as the rifle is canted from left to right. It’s an arc that usually above the target, if the rifle was sighted that way, or beneath it, if not.

                      I once did a big cant test with the readers of my newsletter and we got some great data on what canted rifles do at different distances.

                      Do I need to do a report on the effects of canting?


                    • B.B.,
                      I think I understand the effects of canting better than I can explain it. I would guess that a pellet gun that shoots tight groups at say 50 yards would have horizontal stringing of the group if you were to change the cant for one shot to the next.

  6. Great bog BB, and I am sure you have so much more to say in this area. Over the years I have collected a small amount of scopes and rings, mainly for PBs, but I never seem to have the ‘right’ one when I get a new rifle or pistol. For me mounting optics is work but enjoyable, as long as there is enough time to do it right. Thanks!

  7. B.B.
    This is a very informative report…I only wish I’d read it 20 years ago…
    it would have saved me a lot of heartache!
    One thing I did learn through ‘the school of hard knocks’ is to prevent scope creep through the rings.
    Instead of crushing down with lots of pressure, I get the scope in place with a scope stop to hold the rings,
    then I remove the tops of the rings, one at a time, and put a piece of machinists double-stick tape in the ring piece;
    then I replace that one and lightly snug it down and do the same for the second ring.
    I found this to really help me a lot. *shrugs*
    Perhaps everyone is doing this already and I’m “preachin’ to the choir”…that’s OK. =>
    Again I say, this was a great, and well-needed, report. Thank you.
    take care & God bless,

  8. I have one scope that runs out of adjustment in windage. I think it is left adjustment that runs out. It does this different ring sets, and on different rifles. It’s just an inexpensive NCStar compact 4×30. No adjustable objective. But, I really like that little scope. My eyes have problems, but that little scope gives me great clarity and is quite sharp. I set the front objective focus by removing the front outer ring, and adjusting the objective forward or backward to get a sharp view at my night rat shooting distance of 7 yards. I had to shim the scope to get more left windage adjutment. As I recall, I used a business card to cut strips to shim it. It works, and makes that scope usable for me. It’s like a $20 scope, but I like darn thing.

  9. I’ll jump on the band wagon too preferring a simple 4X scope for general use. Like I said before, one is on my FX Independence. Speaking of which, now you can appreciate that rifle even more now that BB is reviewing the Seneca Aspen PCP. Different quality but very similar in operation. Scope is great when you don’t have the time to make any adjustments prior to shooting.

    It also helps to have a powerful airgun with a relatively flat trajectory but mil-dot reticles will help people who don’t.
    The other thing I like with a 4 power general use scope is having a 35 yard fixed objective. Most of my shots are around that range..

    Two more points of interest I may have mentioned before.

    I have found that the scope ring caps need to be inspected for bore alignment with the ring base. I noticed a very visible off-set when the cap is installed 180 degrees out from it’s intended installation. Something like that could dent your scope. Obviously you check it both ways before installing the scope. Padded rings may negate it, but why take a chance.
    The other is reversing the rings on the mounting rail so the mounting screws are on the opposite side. Especially with all the dovetail variations. It could result in the scope moving slightly left or right of center.

    Tri-focal glasses will definitely screw with your view of reticle lines. They can even make the lines look curved.
    Bob M

      • BB
        Sounds like you should be entitled to handicap points at your next target shooting event 🙂 Heck, and more for being over 70. Lets milk it for all we got ! Floaters are playing hell with my driving.

        ( Entered a question on the Seneca Aspen blog about the hammer spring setting)
        Bob M

            • Bob,

              Treachery eh? I can see it now,…. an old timer comments to a younger shooter,…. “Your going to shoot your gun with it set up like that?”,…. and then walk away, shaking your head.

              Plant the seed of doubt. It could be self defeating. I can see where competition is as much about skill as it is about one’s mental state and confidence.

              On the other hand,… that shooter could be not only be younger (move better),… be highly skilled,.. and have a very solid confidence level. 😉


  10. Off topic]

    Tom, When you get the chance, would you ask airgun manufacturers to PU-LEEZE stop shipping their guns in plastic clamshell holders? It took me 20 frustrating minutes to free my new Umarex 1911 Colt Commander pistol from its clamshell prison, all the time having to be careful I didn’t bleed on the gun from the sharp plastic. At 72, I believe that I, and every other age buyer, deserve better care. Thanks. :^>


    • Joe,

      Good point, I think that they could take a look at the packaging of deli meat, if they want to package the item in a clam shell. Just an easy peel off cover, this would provide a dust proof container to return the gun to after use.

      Just a thought.


    • Joe,

      According to sporting goods sales people that I have spoken to about this issue, that super sealed camshell is as much “childproofing” as anything else. I’m told by them that, until parents stop dropping their children off in the toy and sporting sections of the store to occupy them while the parent shops, we will be faced with really stout packaging to prevent children from getting their hands on stuff that they may not be responsible enough to fool with. Since they can’t resist opening packages that they haven’t paid for, I would say that irresponsible is just the beginning of those kids problems. Having parents, in name only, figures pretty high on that list, I would imagine.


  11. Gerald,

    You are correct that canting will spread the shots horizontally, but it will also spread them vertically a little. I think I need to do at least one report on it. That’s perfect because I have an operation with a short hospital stay coming up next week and I need a report that can be done without going to a range.


  12. I had some of these very issues with my UTG 3-12 x 44 SWAT compact scope that I purchased to mount on my new Gamo Urban. I thought a good option would be a compact scope for the Urban in keeping with the rifle’s light weight of 6.5 lbs. This was one of the attributes of the Urban that I really liked so I wanted to keep the weight as low as possible.

    In retrospect I probably should have gone with the standard size scope because there wasn’t that much difference in the weights. When I mounted the UTG scope with the medium UTG 30mm rings I could not adjust the scope back far enough to get the proper eye relief…bummer. The scope’s bell was also too close to the barrel to allow the lens cap. The workaround for my issue was to purchase a set of BKL offset rings which positioned the scope back far enough for a good eye relief and also gave a bit more needed clearance for the 44mm objective. I could have gone with a cheaper solution but again, I wanted to keep the weight down. The BKL offset rings are of very high quality and fit like a glove to the dovetail rail. Another nice thing is that they self center to the rail. At $49 they were well worth the cost. Here’s a picture of my Urban with the BKL offset rings.

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