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Sighting-in a scope Don’t get carried away!

by B.B. Pelletier

Sighting-in a scope must be frightening to many shooters because, of all the technical questions we get, a large percentage deal with problem scopes. Many of the problems can be traced to the fact that they haven’t been sighted-in correctly.

Problem 1. Sight-in distance IS NOT YOUR CHOICE!
You can choose any distance you like to sight-in your scope, so what can I be saying? Just this – yes you CAN choose ANY distance at which to sight-in, but you aren’t going to like more than a very limited selection of distances. You will be frustrated if you sight-in at ALL OTHER distances, then I will get a confused comment like this:

B.B. I sighted-in my rifle to hit dead-on at 40 yards, but at every other distance the pellet shoots below the aim point! I can understand when it does that at ranges farther than 40 yards, but why does it also shoot lower at 20 yards? CONFUSED

Dear Confused,

Your gun shoots lower at all other distances because THAT’S THE WAY YOU SIGHTED IT IN!! If you want your car to stop within 25 feet of applying the brakes, don’t slam them on at 70 mph!

The laws of physics are more unforgiving than the laws of man.

When your pellet leaves the muzzle, IT IMMEDIATELY STARTS FALLING TOWARD THE GROUND! It doesn’t rise up above the bore and then fall, like the drawings seem to show. It falls instantly, and it falls at the same rate as a pellet dropped from the same height as the muzzle. If the bore is parallel to the earth and the shot and dropped pellets both take off at the same time, they will both hit the ground at the same time. The shot pellet will hit some distance from the gun because of its velocity.

To compensate for the drop of the pellet when we sight-in, we point our scopes slightly down toward the ground, so the exiting pellet will SEEM to rise above the line of sight. That is why we speak of TWO distances at which the pellet will be dead-on with the crosshairs. I discussed this in an earlier posting about sight-in distances (At what range should you zero your scope?).

Here is where physics steps in. Those two distances are determined by the velocity of the pellet AND the rate at which it slows down because of drag. With modern adult airguns all shooting at pretty similar velocities (750-950 f.p.s.) and with diabolo pellets being so similar, the choices of aim points is limited – IF YOU WANT TWO AIM POINTS, THAT IS.

If you insist on sighting-in at 40 yards, go ahead. But don’t ask me why the pellet shoots lower at all other distances. You have selected the spot in the trajectory curve where that will happen. Actually, given a spread of velocities, there is a short span of distances, all hovering around 37-45 yards, at which this will happen.

Yeah, well, B.B., I want to sight-in at six yards, because that’s the distance from my back door to the garbage cans, and we have problems with raccoons. Now, can you tell me why my pellet is so much higher at all other distances? I mean, until I get way out past 50 yards, my pellet is in orbit! Please tell me how to get it back on target at 30 yards, because that’s where the bird feeder is.

ARRRRGH!

[B.B. has left the building – escorted by two nice men in white coats.]

41 thoughts on “Sighting-in a scope Don’t get carried away!”

  1. Tomorow can we get a little rundown on how to determine which ranges our gun/pellet/scope combo like? i understand what your saying in that the way gravity and the trajectory of the pellet work in relation to the scope (and probably more specifically the mounts). but.. how can i learn where the proper place to site in at is?

  2. BB,

    yesterday I got a huge scope with a R14 reticle. Besides the normal mildots it has additional lines useful for greater hold over at very long distances. The sighted in distance is less important – just remember the right POI at the current magnification.

    Is there an easy way to center the scope straight above the barrel? Something like a plumb line at the objetive?

    Markus

  3. Markus,

    By “centering” the scope, what do you mean? Bisect the rifle with the vertical reticle, when the rifle is level? That’s impossible, because there there are infinite ways of determining level on a rifle.

    I could go on but let’s cut to the chase. The best way to level a scope is by eyeball, letting the vertical retical bisect the rifle’s action. Unless you do that, the scope will always look canted to you and it will drive you nuts.

    Once you are happy with how the scope looks to you, you can also check the level against a plumb line at distance. Align the vertical reticle with the line and you’ll be able to tell if it’s level or not. What THIS checks is the level of the scope when the gun is rested or being held. It’s actually a means of leveling the rifle, since the locked-down scope now provides a datum.

    B.B.

  4. BB: If you are back in the building now (LOL), I’d like to ask what range my new RWS 34 .177 using 7.5g Crosman premiers and a Tasco Golden Antler 3-9×32 should be sighted at.

    Thank you

  5. one word for this post…
    “MILDOT” I’ll never buy another airgun scope that isn’t. Leapers even puts the dots out farther than any other scopes Ive bought (on my cheepo budget)

  6. ben,

    The ballistic coefficient refers to a projetile’s aerodynamic performance in air. A spear as a higher coefficient (is more aerodynamic or slippery) than a bowling ball.

    Determining the BC requires measurements of velocity at given points and plugging them into an equation.

    B.B.

  7. B.B.,

    I would suggest a more clearer, step-by-step explicit procedure in sighting-in a scope on an airgun.

    We read mostly in general terms about the process. For example, most articles on sighting-in do not even mention that the barrel must first be horizontal and level with the ground.

    Then, for zoom scopes, at what power level we must set, minimum or maximum? Of course a zero remains the same but at different magnifications, the sight picture as we look thru the scope is different at 4x and at 24x.

    Also , scope height from the center of the bore also matters. These and surely more I learned the hard way, trial and error.

    I clamp my rifle on a vise when I zero, is this a reliable practice?

    I do not have a chrono, I do not know my pellet’s BC, how do I zero my scope?

    How did Daniel Boone zero his long Kentucky rifle, without BC, chrono, nor a ballistics program on a computer?

    Thanks.

    Dave

  8. Thanks BB for your advice that my conceept is futile. I plan to attatch a level to my scope to avoid canting after I figure out how to level my rifle.

    Mostly I have the problem that I miss to the left or to the right when I shoot at other distances than the one I sighted in.

    Markus

  9. Markus,

    A miss to the left or right can be many things besides the scope. Using the wrong pellet will sometimes get you a spiral (helical) flight path that defies belief! The pellet actually “corkscrews” to the target. I have seen it several times when the light was perfect. The cause is instability.

    And have you read all the past posts about scope problems? Your answer might be there.

    B.B.

  10. Markus,

    A miss to the left or right using a scope can be caused by parallax error. This is when changing positions of your eye changes the point of aim of your scope. (If there is parallaz error the crosshair moves around if you move your head from side to side without moving the position of the scope – it looks like the crossharis is sort of floating.) It is a function of distance. Adjustable objective scopes allow you to set the scope to be without parallax error at whatever distance you are shooting. If this is set incorrectly parallax error will still be present (the yardage indicators on the scope are often incorrect in my experience.

    You mention having a “huge scope” with “lines useful for greater hold over at very long distances”. This makes me think you have a firearm scope mounted on your air gun. Scopes for firearms are often set to be parallax free at 100 yards. When shooting at distances under 100 yards, especially in the 10-50 yard range we shoot airguns, parallax error can be a big problem with these scopes. (Parallax error is not nearly as much a problem as the distances become greater. For example, the difference in parallax between 200 and 300 yards is quite small.)

    I’m willing to bet Daniel Boone set the zero on his rifle by shooting a lot and learning his gun – something we should all be doing rather than sitting in front of a computer screen. 🙂

    Ehrich

  11. Dave and everybody else who has troubles sighting-in,

    I will do a sighting-in series! I will include scopes in my series!

    I have already done most of this in past posts, but I will try to organize this series so that it makes more sense. The internet is currently FLOODED with discussions about sighting in. Some people have wriytten formulae about how to sight in that include the height of the scope above the bore and other things.

    I believe I can simplify things a lot, but we’ll see. This series will all be linked, like the spring tuning series, but it will not necessarily run on consecutive days.

    B.B.

  12. BB,

    I just wanted to say thanks.By reading this daily post I beleve ive become a better shooter.Because I dont have to guess ehat im doing.Yesterday I read the shooting positions and technics.And used them exept for the light hold because its a gamo cf-x.And ive been shooting since january and yesterday I made my best group.5 shots at 30 yards that were 1/2 inch.Maybe for some people that is a normal group size but for me its a big improvement and I know its because of you BB,so THANK YOU.

    Hernan(CF-X guy)

  13. Hernan,

    Thank you for that report. I write this blog for shooters like you who really want to enjoy their sport. I remember how difficult the decision to buy the CF-X was, and now you are doing so good with it.

    My only request is that you help others enjoy airguns as much as you do. As I recall, you have a friend who is watching what you do and rreading this blog. He is the perfect place for you to start!

    Thanks,

    B.B.

  14. BB,

    I forgot to tell you.My frien william and my beest frien Eric both both gave me the money and I got a gamo shadow varmint hunter with a leapers 3-12×44 like mine and william got a gamo shadow 1000 red dot and mounted a leapers 3-9×40 scope.They love the sport and I always tell people about the sport.At least 2 friends are shooters now.And I thank you because this is the best place in the world for airguns.And ALL ive learned is thanks to you and since my friends dont have internet I read the blog every day and tell them about it.THANKS FOR EVERYTHING

    Hernan(cf-x guy)

  15. I have twin girls, age 12 who are in Air Cadets and use air rifles as part of their training. Do I get them an air rifle with or without a scope. Is it easier to just use open sites to attempt to hit something at any distance than always shooting from a scoped in distance.

  16. I’m thinking that the Air Cadets probably use open sights in their training. If so, you should, too.

    Open sights are somewhat quicker to use, plus they are fundamental. Shooters should learn to use them first.

    I don’t know what training the Air Cadets offer, but I would think a Daisy 853 or Crosman Challenger 2000 would be right. Both of these are youth target rifles and they have aperture rear sights, which are more precise than sporting open sights.

    B.B.

  17. Okay,

    That’s not a laser sight. it’s a red dot sight and has nothing to do with lasers.

    Yes, dot sights will work on breakbarrels, but this grade of sight isn’t made to take the punishment a breakbarrel dishes out. Try something like the Gamo or Leapers brand. And don’t forget that most breakbarrels require a sight that fits 11mm dovetails.

    Dot sights usually have no magnification, so they are quicker to pick up when hunting. On the minus side, they are less precise than scopes.

    B.B.

  18. hi there i just bought a new scope for my 22 rifle and i am planning to put my old 22 scope on my springer can i do that and is it going to mess up my scope??

  19. heyy bb i just bought a 3-9×32 scope for my beeman pellet rifle…started sigting it in today and at 10 feet i was in like on they y axisbut about 6 in high..after a while i got to about 15 yrds.i was shooting a foot high…after adjusting the scope as low as it would go all i could do was shoot for a dot and hit 6 in. above it.. any advice?

  20. Y axis,

    You don’t mention the model of airgun, but I suppose it doesn’t matter. You have a rare type of barrel displacement that is the opposite of barrel droop. Your barrel shoots higher than it should. This is so rare that I have never talked to anyone who actually had a gun that did it.

    HOWEVER – this condition is easily caused if the barrel was allowed to snap closed without restraint – assuming it’s a breakbarrel, of course. In that case, the barrel is bent upwards and needs to be straightened. Has that happened while you owned the rifle? Was it a new rifle? Did you buy it from a store where a customer may have done this (fired the gun with the barrel open)?

    If the barrel is not bent, but only misaligned in the receiver, an adjustable scope mount will correct the situation. You elevate the front ring instead of the customary rear ring.

    If the barrel is bent, it needs to be straightened before trying to deal with the sight-in.

    B.B.

  21. What do you exactly mean by two sight in points?! I sight my 1250 fps rifle in at about 30 yards with a tasco scope, on the lowest magnification, then at any other point I would be to low and have to compensate the shot? Please explain, not a physics lesson

    • Pretty much any explanation is going to be a “physics lesson”.

      Take a piece of paper and draw a wide (but not too high) parabola (with the “cup” down)

      __/———-\___

      Pretend that is your trajectory (and that the barrel is aimed slightly upwards.

      Your sights are about 1.5″ above the left hand starting point, and make a line straight across. That means all shot close to the gun are below the line of sight until the upward slope intersects the line of sight (first/ascending zero). It will be above the line of sight for some distance and the trajectory stops rising and starts to fall again. At some distance it will cross the line of sight (second/descending zero).

      If you adjust the line of sight/barrel angle you can move the first zero further away — but that also brings the second zero closer. At some point both zeros intersect. All shots will be low except at that distance — as that distance is where the projectile stops rising and begins to drop (relative to the line of sight; it has been falling relative to the bore line all the time).

      If you figure out how far above and below the line of sight you are willing to accept for “no adjust” aiming, you can select zero point(s) to maximize the range.

      Forgive the use of a firearm, I just don’t have figures for airguns handy, but did do some research for the carbine: .44RemMag from a lever action carbine. A 75 yard (second) zero just manages to also provide a 25 yard (first) zero. Between 25 and 75 yards, the bullet is a bit above the line of sight (less than 2″ as I recall — this is meant as a short range/brush deer gun, where the target area is a 4-6″ circle, so 2″ above at the midpoint, center at 25 and 75 yards, and 2″ low closer than 25 [scope is only 1.5″ above, so that’s the lowest the close point gets] and out to 85-90 yards for the far end)

      Just pumping numbers into ChairGun: .177 with AA Field 8.4gr at 1100fps (a bit high for lead in even a magnum spring gun), scope 1.5″, and 1″ “kill zone” (+/- 0.5″).

      44 yard (second) zero gives a (first) zero at 17-18 yards, and “point blank range” of 10 to 50 yards. The pellet is no more than half an inch low between 10 and 17 yards, and from 44 to 50 yards. It rises to half an inch high at the mid-point between 17 and 44 yards.

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