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How to tell if my zero is shifting?

 
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  #1  
Old 03-16-2005, 04:59 PM
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Join Date: Apr 2004
Location: Northern California
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How to tell if my zero is shifting?

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 [img]/ubbthreads/images/graemlins/wink.gif[/img]and were ever else it wants to go?
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I shoot 1/4 inch groups at a 1000 yards. That is...till my second shot.
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  #2  
Old 03-16-2005, 07:55 PM
 
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Re: How to tell if my zero is shifting?

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.
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Old 03-17-2005, 10:48 AM
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Re: How to tell if my zero is shifting?

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?
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I shoot 1/4 inch groups at a 1000 yards. That is...till my second shot.
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Old 03-17-2005, 02:12 PM
 
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Re: How to tell if my zero is shifting?

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.
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  #5  
Old 03-17-2005, 03:27 PM
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Join Date: Jun 2007
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Re: How to tell if my zero is shifting?

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.
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Old 03-17-2005, 04:52 PM
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Re: How to tell if my zero is shifting?

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.
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  #7  
Old 03-17-2005, 05:42 PM
 
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Re: How to tell if my zero is shifting?

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.
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