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Old February 9, 2012, 10:58 PM   #1
Jerry45
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Question about variable power scopes.

I have several and they all seem to shoot POI = POA no matter what power setting I’m using. Granted I don’t shoot one hole 10 round groups but they do group. I read something the other day that made me go hummmm. Someone giving a review on a scope wrote that there was only minor deviation (1 ¼” to 1 ½”) at 100 yards from 8 to 32 power, which he deemed acceptable in a lower cost scope. None of my scopes were “expensive” and I’ve never noticed and change of POI v POA at any distance. Does the guy now what he’s talking about? I ¼” to 1 ½” shift in POI by changing the power setting?
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Old February 9, 2012, 11:11 PM   #2
ScottRiqui
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Well, POI obviously shouldn't change with a change in magnification alone, since you're not moving the barrel, but I could see how POA could change with magnification if the optics inside the scope were misaligned.

Rather than actually shooting groups, an even simpler alignment test would be to clamp the scope in a vise while it's aimed at a piece of graph paper, and then see if the crosshairs move across the paper at all as you adjust the magnification.
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Old February 10, 2012, 12:33 AM   #3
Jerry45
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Since I have the same model scope on order that he gave the review on I’ll do as you say before mounting it. I’m interested to see what it’ll do. The scope received very good reviews (read all I could find before ordering) and the gentleman also gave it a good review with that one exception. Actually he didn’t seem concerned with it saying it was acceptable to him. If my scope did that it would concerns me.

I just pulled one (another brand) off my 06 that has a parallax problem. POI shifts 2 to 2 ½”. That’s without increasing or decreasing power. Put another scope on the rifle and it (I on a good day) shoots ½” 10 shot groups at 100.
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Old February 25, 2012, 01:34 AM   #4
Clark
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http://www.youtube.com/watch?v=KJXO8kaXfJI

This is my 10 second view of a Leupold Zero Point.

I am twisting on the turrets for 10 seconds, but to see the change in point of aim with magnification, I would have to screw on the magnification.

I can't make another video quickly showing that, I need to set up the camera on a two rack and pinion gears to keep in the the visual box.

I have a 30 minute video on how to modify the Leupold Zero Point, to use a different LED and battery pack.

http://www.youtube.com/watch?v=Wu0XPNETm1U
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Old February 25, 2012, 08:13 PM   #5
Jerry45
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Clark, thanks for the video’s. I’m jealous of your machining equipment.

The scope is a Lapers 8-32X56. I could not see any change up down right or left by rotating the magnification knob. I mounted it on my Savage .17 HMR. With it set on 20 I fired one shot at 25 yrd. 1/2” high 2” right. Had my wife rotate the windage knob while I held on target. Second shot center ½” high. Fired again and put it in the same hole. Ran the target out to 50 yrd. Cranked up to 32, center ¼”(?) high. Ran it out to 100 did a minor tweak for dead center, then zeroed the turrets. Played with the magnification and all shots grouped under 1”. Started shooting “empty” shotgun shells and ¼” size pieces of clay pigeon on the 100 yrd. burm. POI v POA does not change.

The scope was advertised as “used like new” on Amazon.com. So I took a chance. It was like new and the turrets had been rotated but as you can see it zeroed easily and finish and function is perfect. Only time will tell how good they really are but as of now I really like these scopes. I have four, a 1-4x24 on my 45/70. I’ve fired about 30 rounds with it mounted and it's holding up. A 3-12x44 on my Sig 522, 4-16x56 on my 06 and now the 8-32x56 on the 17. So far they have proven to be accurate and tough. I had the 1-4 on the 522 and my grandson knocked it over on a concrete bench on to the windage knob and it held zero. Now on the 45/70 it’s taking a beating.
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Old February 25, 2012, 08:59 PM   #6
Jim Watson
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Forty years ago, POI shift with power change in variable scopes was a hot topic. It was considered usual in all but the very best. The recommendation was to zero your scope at maximum power and hope the shift was insignificant at lower power for closer or larger targets.

Scopes are more precisely made now, even the cheap ones.
I would grumble about a 1.5" shift... but not too much in a Leapers.
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Old February 25, 2012, 10:00 PM   #7
Jerry45
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That makes sense. Perhaps I’ve never noticed it in any of my scopes because I’ve never sighted one in at the lowest setting.
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Old February 26, 2012, 01:28 PM   #8
Clark
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There must be some trade offs in variable power scopes:
Cost
weight
accuracy
reliability
effort to get the design right

For a long time I saw scopes with 3 to 1 power ranges, and then they suddenly got bigger a couple years ago. Some of those early high ratio low cost low weight scopes were showing up in qualities as refurbished. I don't know if it was the extra power range or not that was the problem.

scroll to the bottom of the page and look at the pics off all what has to scroll in the scope
http://bulletin.accurateshooter.com/tag/scope/
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"Ad hominem fallacy" is not the same as point by point criticism of books. If you bought the book, and believe it all, it may FEEL like an ad hominem attack, but you might strive to accept other points of view may exist.
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Old February 26, 2012, 06:50 PM   #9
Jerry45
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Thanks again Clark, good stuff. I save the link in my favorites.
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