How to tell if my zero is shifting?

Discussion in 'Long Range Scopes and Other Optics' started by Kenster-Boy, Mar 16, 2005.

  1. Kenster-Boy

    Kenster-Boy Well-Known Member

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    Other than just the bullet impact is there any way to distinguish if the zero is bouncing around in my scope and it is not just the tempurature, altitude, wind, barometric pressure, gravitational pull toward the equater /ubbthreads/images/graemlins/wink.gifand were ever else it wants to go?
     

  2. Guest

    Guest Guest

    A faulty scope that will not hold its zero will almost always shoot two different groups. One round will alternate with the other. For instance, at 100 yards, the first round will impact at 7:00; the second will impact at 2:00 and repeat itself. This is a classic example of a failure. Another example will have the groups making an overall “V” pattern. If you are shooting 1” dots that are from left to right on the target paper, (let’s say five dots in a row) the pattern made can appear as a slight “V.” Another scenario is that if the interior spring(s) inside of the scope have completely fatigued altogether, your group will be all over the place; I mean 8” groups at 100 yards!

    If your rifle is not properly bedded, it will shoot two lateral, left to right groups. Make certain though that it is not a poor quality rifle or barrel. Barrels, once rusted inside will never shoot well again. Also, a factory grade barrel will shoot the first two rounds fairly close together, but once it heats up, the third or fourth round and every other round after that will walk / hit approx. 1” to the right.
     

  3. Kenster-Boy

    Kenster-Boy Well-Known Member

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    thanks that gives me a better idea. For the most part when ever I take the gun out to shoot it seems to make a descent five shot group (1 - 1.5 inch) at 100 yards but it never seems to be as on target as it was the time before. Like the other day I went to the range and shot a 5 shot group that was 1 inch high. That just will not cut it for long range shooting.
    And as you mentioned you will get two sub groups. I was having that happen at 200 yards or at least it was a little more aparent because 3 out of 10 shots didn't drop at all when the rifle was sighted for 100 yards. so in other words I had a 3 shot group in the bullseye and a 7 shot group about 3 inches low. Could this be a shifting zero?
     
  4. Guest

    Guest Guest

    Not to offend you, however a 1.5” group at 100 yards is terrible. It is caused by a combination of rifle, i.e. bedding, stock, trigger, firing spring pin and scope; Internal and external ballistics. If the spring is worn out, the lock up time will be slower and the accuracy will be affected.

    Another area of maintaining your zero can be affected by the light and wind. If you zero in full sun-light and then shoot in an overcast condition, (shadow effect) your poi will be ½” low at 100 yards. Add a tail wind of five mile per hour or so, and again, poi will be low, approximately ¼”. If the sun is at 9:00, poi will be ¼” right. If it is at 3:00, poi will be ¼” left.
     
  5. 4ked Horn

    4ked Horn Writers Guild

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    W could you explain this shadow effect and what causes it? I have never heard of this. Is it happening inside the scope due to the light coming in from the top or sides of the Obj lens? Or is it happening outside the scope from the way the light hits the target its self.
     
  6. Kenster-Boy

    Kenster-Boy Well-Known Member

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    W, I take no offense to the fact that you think that a 1.5 inch group at a 100 yards is terrible. I must explain that the rifle is capable of much better I have shot it in the .5 to .75 before but only on perfect condition days with no wind no mirage and a good solid rest. Most days the conditions are a little more adverse where I shoot and shooting out of the back of my pickup isn't exactly ideal either. I also shoot 5 shot groups and measure outside edge to outside edge of the holes. (not that that makes any huge difference or anything but for prides sake let's say it does)
    Bottom line is that I am not capable of a much better average than 1 inch. I don't beleive that the gun itself is the problem although a factory savage 112 BVSS is only as good as any other stock rifle could be. Although if you have any suggestions as to some minor ajustments that could be made to increase the accuracy of my rifle I would be open to the possibility of having my brother (a gunsmith) alter it. I don't want to ask him to do anything profound with the gun since he already thinks that savages are salvages but small things such as re-crowning could be a definite possibility.
     
  7. Guest

    Guest Guest

    7mmag man:
    You may want to give George Gardner a call (or a try for that matter) at GA Precision in North Kansas City, Missouri. He is one of the Most Competent Gunsmiths around. As long as you have good glass (Night Force or similar) mounted onto it, his rifle(s) will shoot phenomenally well. If you get a chance, ask Ian McMurchy, he owns at least one of them.

    I am not that familiar with Savage’s, (except the model 99)however a friend of mine owns the tactical model in .308, and out of the box, it shoots pretty well.

    4ked Horn:
    As far as explaining the “Shadow Effect,” I do not claim to have a PHD in optics; however I do know that the shadow effect is caused by secondary and refractionary light waves as they pass through the eleven lenses of the scope. Have you ever put a pool cleaning screen or a stick into a body of water and watched how the image bent? When the light passes through the lenses, it is similar to passing through a prism. The image is slightly repositioned from one lens to the other; I think the term is known as “phase.” We’d need a Scientist to explain it better than that.
     
  8. JonL

    JonL Active Member

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    Hey,

    I've read some reviews about the GA Precision rifles at Sniper Country. Them guys really like them.
     
  9. winmagman

    winmagman Well-Known Member

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    7mmMag man
    If the Savage is a pre-Accutrigger model probably the best thing you could do for it is get a Sharp Shooter Supply after market trigger, that in itself makes a huge difference. I did the same thing for mine.
     
  10. Guest

    Guest Guest

    GA Precision... Phenominal reputation, Christiansen arms too. However, I am waiting for my new 6.5 x 284 to arrive from GA.
     
  11. 4ked Horn

    4ked Horn Writers Guild

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    Thanks W that makes sence somewhat. I'll have to look into it a little further.
     
  12. Waltech Jim

    Waltech Jim Writers Guild

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    7mmagman,
    [ QUOTE ]
    I must explain that the rifle is capable of much better I have shot it in the .5 to .75 before but only on perfect condition days with no wind no mirage and a good solid rest. Most days the conditions are a little more adverse where I shoot and shooting out of the back of my pickup isn't exactly ideal either.

    [/ QUOTE ]

    I wouldn't be looking for problems with any of my shooting equipment if I was shooting out of the back of a pickup.


    [ QUOTE ]
    Bottom line is that I am not capable of a much better average than 1 inch

    [/ QUOTE ]

    Not flaming here, but if you aren't confident in shooting less than 1", I certainly would not spend a lot of money on improvements to your rifle.

    My suggestion would be get that gun and yourself on a SOLID rest, where you can spend some time with someone that can help you get confident with shooting less than 1". Only after taking care of this, would I judge the equipment.

    Jim
     
  13. Kenster-Boy

    Kenster-Boy Well-Known Member

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    Winmagman I appreciate the tip on the Accutrigger but my rifle came with one. I bought it new last year.

    Waltech,
    I have planned a trip to the range tomorrow to achieve some of what you have mentioned. They have good solid bences and a true 100 yard range. I have a bipod and some sanbags made up so it should be a start in the right direction. Although I am not as worried about the small movements at 100 yards as I am the two sub groups at 200 yards as I had previously mentioned. Maybe I am all wrong and my handloads are off. But I have been extreamely careful in my loading process so I kind of hessitate to say that it is a possibility.
    As for spending a lot of money on my equipment it would be free to have my brother modify it because he already offered to put a match grade crown job on it for me and he is a competent gunsmith.
    The only reason that I have jumped to the conclusion that it may be the scope is because it is a Leupold 6.5-20 with target knobs and the first week that I had it I had to send it back because the ajustments weren't working properly and maybe I just thought it a good scapegoat to start with.
    I will give an update as to how the shooting excursion goes tomorrow and maybe it'll help you all diagnose the problem a little easier.

    Thank you all for your input!
     
  14. Guest

    Guest Guest

    Waltech Jim: Quick and true story. Several years ago I worked with the Hollywood Celebrity Shotgun Shoots Executive producer, "John Laughlin” and his publicist, “Michael Conely.” Michael wanted to shoot as he had never shot any kind of a firearm or BB gun for that matter in his life and was formerly a publicist for the Disney Organization and before that, the Vatican. To make a long story short, I spent about twenty minutes or so teaching him just how to hold the Rem. 700, chambered in .300 Win Mag, and resting on it's Harris Bi-pod. I set him up on a 6” diameter Ram’s head at 400 yards, dialed in the dope and had him pull the trigger. He hit dead center. He couldn’t believe it and Laughlin’s jaw was hanging on its hinges. The next round hit the same spot. The third round hit dead center at 500 yards followed by another center hit at 600 yards. If you think that I am telling a story, please contact Mr. Laughlin, he will confirm it. The build and components of the rifle accompanied by pro grade optics, such as Night Force, and quality ammunition is the foundation of accurate shooting.