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Scopes Explained

Discussion in 'Stickies Only' started by Airguninfo, May 22, 2009.

  1. Airguninfo

    Airguninfo Moderator

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    By popular demand I am going to try and take the mystery out of telescopic rifle scopes.
    I am going to use the scope that I have on my AA410 for demonstration purposes. But that does not mean that the things I write down do not apply to other scopes of different specifications.
    We will have a look at the different kind of scopes that are out there later in this post.
    Scopes are, basically a tube containing several lenses, sometimes as many as eight, set apart from each other within the scope. Somewhere in the middle of that lot is a thing called a reticule – this is what you place on your target. The middle of the reticule is the spot where the pellet should hit the target at a fixed distance. Why at a given distance?? Well the centre of the reticule ( cross hairs ) is the straight line of sight. But unfortunately, the flight path of out pellet is not that straight but curved. With the centre of the scope being above the centre of the barrel, the pellet will have to cross out line of sight twice. Once on its way up from the muzzle through the line of sight then it reaches the top of its trajectory (and this is the bit where Isaac Newton takes over*1) and comes through the line of sight again as it starts to drop. It is important to understand this bit as we will need this when we determine the distance to which we zero out scope.
    But first of all we have to mount the scope to the rifle. If you have a spring rifle you will have to make sure, that the scope you are buying is rated for spring rifles or the two recoils that these things have will make it a short lived pleasure to use as they can knock a scopes reticule out of alignment or worse.
    When we fix the scope to the rail on the rifle, it is important, that we get the distance to the eyepiece correct while we have the rifle shouldered in a comfortable way. That is without craning out neck or having to hold the rifle up and half way of the shoulder, because we need to have our eye at the right height and distance from the eyepiece to get a clear picture when we look into the scope. Do spend a bit of time sorting this out as it will make everything later a lot easier. Also try to get the scope mounts as far apart as you can as this makes for a more stable fixture of the scope on the rifle. Make sure that you get the cross hairs vertical and horizontal when you hold the rifle so they look like a cross and not like an X( *2) . If you don’t have 100% vision like me, you may have to adjust the focus of the eyepiece to get a clear sight picture. Once you got this lot sorted we can start to find our zero.
    How to zero scope?
    Let’s say, that we are going to use our rifle for hunting. That means head shots on rabbits and co. So the bit we want to hit is about one inch in diameter and our effective range is out to about 40 yards, using a sub 12 ft/lbs rifle. I want to shoot without having to play about to much with hold over or under so this is the way that I have set up my scope.
    My scope has a 50mm lens on it and the centre of the scope is 1.6 inches above the centre of the barrel and my comfort zone with head shots is out to around 40 yards. First off, I set up the gun on a stable platform (sounds great for a garden table) and set up a target 10 yards away. Now I take one shot aiming at the middle of my target ( A4 sheet of paper with a dot in the middle *3)
    If you miss the paper all together at this point you will have to get closer, but as a rule you will hit it with the first shot. Lets say, that you hit the target 3 inches low and 2 inches to the left of the dot.
    Now you need to take the covers of the turrets and under them you find two dials. As a rule they have a little arrow on them with the elevation dial saying up and the windage dial saying left. Using the windage dial we turn it about 10 clicks to the left as we hit the target to the right and take another shot. We work our way to the centre of the target step by step. The same thing goes with the elevation dial. As we hit the target low, we want to turn the dial up a few clicks at the time until we get to the centre with both and hit the dot. Now we put up a new target and shoot a group of five shots at the dot and see if we ended up where we wanted to.
    Unless you have a big garden it is now time to move into the field for the rest of the zero session.
    Having made the decision of the size of my target being one inch, I need to find the distance that my pellet will travel within this zone. I have used a program called “Chairgun” to work this out and by chance the 10 yard first zero was spot on in my case and all I had to do was to confirm what I had worked out at home. If you want to work it out on foot you will have to set up your targets in distances of 5 yards from 10 to 40 yards and find out how much over and under zero you are at those distances by aiming at the dot in the middle and seeing where your pellet ends up on the target.
    So my pellet is 0.5 inches under zero at 7 yards passes through zero at 10 yards for the first time, is around 0.5 inches over zero at 18 yards passes through zero at 28 yards and ends up 0.5 inches below zero at 34 yards. This is using AA fields in .22 and running at 11.5 ft/lbs. This keeps the point of impact within an inch from 8 out to 34 yards. By the way, the Chairgun program if free and you can download it of the Hawke web site. I think it is a good tool to use.
    Let’s have a look at a Scope for air rifle shooting and what is this parallax thing anyway??

    [​IMG]

    1 Objective bell
    Scopes come in different sizes and the larger the diameter of the fist lens, the more light it can gather. In this case it is 33mm and has the parallax adjustment at the front objective ring. (I will come to the parallax bit later).
    2 The two turrets for the adjustment of elevation and windage. The bits that we use to zero the scope. When you are done with any adjustment, put the dust caps back on as you don’t want any grit in there. Lets have a closer look at the turrets (in this case the elevation one)

    [​IMG]

    On it you see, the arrow for the way you want to turn it if your shot hit the target low and the value of one click of the adjustment ring.
    It says one click is 1/4 MIN. One MIN or MOA means Minute Of Angle and one minute of angle at 100 yards is one inch. So in this case one click is a quarter on an inch at 100 yards or or in out 10 yard zero session its 40 clicks to raise or point of impact by one inch.
    3 The magnification ring
    This is like the zoom on a camera and lets you adjust the magnification of your sight picture. In this case from 3X to 9X. But there are scopes with fixed magnification as well and If you buy one of those, a 4 to 6x magnification is a good compromise.
    4 Ocular Bell
    If you mounted the scope correctly, this is the bit you will be looking into and you can adjust the last ring of the scope to suit your eyes. You can’t see it on this photo as it is covered by a eyepiece extension. These extensions help to place the eye faster and in the same position behind the scope.
    Most scopes for the use with air rifles have no adjustment for the parallax and it is fixed to 35 yards. If however your scope has this adjustment you can use it for finding your range and more accurate shooting.
    Basically, you have two focal planes. One is on the target that you look at and the other is your reticule. Using the parallax adjustment you can put both on the same plane and the sight picture will be sharp with the reticule being like it is painted on the target. If both are on different planes you can be a fair bit out with your aiming depending at what angle you look through your scope and your eyes will try to focus on either the target or the reticule.
    How to use it for range finding.
    Pick a spot that you know the distance of then set your parallax adjustment to that distance and now you adjust the eye lens so that you get a sharp sight picture. From now on your scope will give you the range to the target every time you focus the sight picture using the parallax ring.
    [​IMG]
    (Some scopes have the adjustment for the parallax on the side like a third turret)


    Let’s take a look at some different reticules that are out there these days.

    [​IMG]

    Fine: This is the grandfather of all reticules and the one that gave them the name cross hairs even though the “hairs” where usually made of thin wire. These are still widely used today for hunting, as they allow for quick and uncluttered target acquisition and are easy to read. The problem with these is that the fine lines can be hard to see in low light situations like when we are out lamping.
    Duplex: If you are after a simple easy to use sight then this is the one to go for because the thicker posts will make it easier to see in low light conditions but you will still have the fine line of the cross hair to allow for accurate shot placement.
    Post: This one was invented in Germany during the Second World War and pretty much a standard for snipers in those days. I am not that fond of them, not because I am German but the thick post is a bit of a bummer when using hold over on small targets like a rabbits head because it covers the bit one wants to hit.
    Dot: I am not that fond of this one either because of the comparatively large area that is covered by the dot.
    Mil-Dot: This is my favourite and has been for a number of years and I had them on most of my rifles up to now. Once you get used to this reticule it takes a lot of the guesswork out of hold over and wind drift by using the dots on the cross. Another plus of it is, that one can use it for range finding within limits.
    Circle: Here is another leftover from the war. This reticule was adapted to telescopic sights from the open wire construction used on heavy machine guns when used with tracer ammunition. I don’t think it is of any use for hunting, but whatever floats your boat.
    There is a multitude of different reticules out there and to be honest, some of them resemble a map of the London underground and I find them more confusing than anything else for hunting, but they do have their uses for the target shooter. But as I said earlier, whatever floats your boat
    Illuminated or not is a question you will have to ask your wallet. Whatever reticule you want in your rifle they are all black when using them during the day but with a IR you can make shooting at low light and when out lamping just that little bit easier.


    *1) Isaac Newton is the bloke with the apple and the inventor of the cat flap
    *2) Yes I have seen that done
    *3) I aint rich you know

    I hope that this has cleared up a thing or two about air rifle scopes. If there is something that I have left out or explained in a bad way, drop me a line and I will try to edit this post or add to it as needed.
     
    Last edited by a moderator: Jun 20, 2009
    marlever357 likes this.
  2. Jiggy ward

    Jiggy ward Donator

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    cheers mate
     
  3. steve410

    steve410 Big Poster

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    Nice one,I have made this a sticky.I think a lot of people will find this very helpful.Thank you for putting the time and effort into this.:up::)
     
    marlever357 likes this.
  4. Airguninfo

    Airguninfo Moderator

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    Not a problem helping and getting help is what we are here for.
     
  5. methuzula

    methuzula Engaging Member

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    Wondered what just happened, I answered the wrong post but seeing its moved it now makes sense.

    Good post.
     
  6. i8allthepies

    i8allthepies Posting Addict

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    Top post :up::up::up: I'm sure loads of people on the forum will get benefit from this.
     
  7. Jiggy ward

    Jiggy ward Donator

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    scoba i posted on other thread that started this look on www.hawkeoptics.com they have done one to download its about the airmax map using .177 and .22 theres grafs/graphs
     
  8. Airguninfo

    Airguninfo Moderator

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    Yes mate its the Chairgun program that I mentioned in that post.
    Thank you for putting up the link.:up::up:
     
  9. Dave_Cossy

    Dave_Cossy Engaging Member

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    Great Work

    Thanks for taking the time to write the thread, it's good to learn and refresh what we think we know.
    Good work fella.
    :up:
     
  10. Airguninfo

    Airguninfo Moderator

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    Funny you should say that, but I found when I was writing this post, that I don't tend to think of a lot of things that I do as they have become second nature. But I only found out by actually writing them down. It's a bit like driving car, you don't have to look at the gear leaver to know what gear you are in unless someone else wants to know and that gets you thinking about it. So it got me back to thinking as to why I do things the way I have done them for so many years.
     
  11. Carrot Cruncher

    Carrot Cruncher Engaging Member

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    Top Man

    Thanks a lot for that scub, this has cleared a lot of Q's and A's that I had. If I had posted all my questions then we all would have been here all year lol

    Thank a lot mate

    Bloody good work :up::)
     
  12. Airguninfo

    Airguninfo Moderator

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    Well just post the Q's that are still left over and I'll give it a go puting the A's up for them.
     
  13. andyhawkx3

    andyhawkx3 Major Poster

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    Good write up. ;):up::D
     
  14. joeblacky

    joeblacky Well-Known Member

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    great post :up:
     
  15. Tadpole

    Tadpole Super Moderator Staff Member Mod/Admin

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    Many thanks, enjoyed reading this information, essential for us new guys on the block :thumb:
     
  16. guns guns guns

    guns guns guns Member

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    Good Write Up

    helpful to us newbies :confused:
     
  17. robbed666

    robbed666 Newbie

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    As a 'Noob' here, thanks for the great info.:cool:

    I'm just setting up the scope on my new gun.
    One thing I did find, the positioning of the scope on the gun is also crucial. Eye piece to eye distance, finding the stock to soulder postion not only for comfort, but head postion is also very important.

    There is a 'sweet spot' in the above that needs to be achieved.
    especially if both physical and eye 'fatigue' is to be minimzed.

    Just my 2ps worth.

    Rob
     
  18. arbab

    arbab Well-Known Member

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    What's the lowest mildot scope, AO, which is not made in China? TIA for any input
     
  19. Vin0bim

    Vin0bim Newbie

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    Nicely done
     
  20. Bootsox

    Bootsox Member

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