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Changing magnification on rifle scope

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kphunter View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kphunter Quote  Post ReplyReply Direct Link To This Post Topic: Changing magnification on rifle scope
    Posted: October/27/2007 at 22:32

When I'm shooting at the range at 100 yard targets, I prefer to crank up the magnification on my Leupold VXI 3x9x40 scope to 8 or 9x.  Once I've completed my shooting at the range, I'd like to change the magnification back to 3x or 4x for hunting.  Will this change the point of impact of my rifle if I do this?

 

Thanks in advance for your answers!

 

KP

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Post Options Post Options   Thanks (0) Thanks(0)   Quote www.technika.nu Quote  Post ReplyReply Direct Link To This Post Posted: October/28/2007 at 00:22

It can possible do that as you have a second plane reticle in that scope.

But some testfiring at high and low magnification will qiuckly tell you if you got a shift problem in the scope or not.

 

Regards Technika

 

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RONK View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RONK Quote  Post ReplyReply Direct Link To This Post Posted: October/28/2007 at 12:52
All the Leupolds I've used over the years have been very consistent in holding zero throughout the entire range of magnification. That is really an impressive engineering feat when you stop and think about it. By all means though, always test YOUR scope from a bench to make sure that YOUR scope holds zero at various settings, as Technika suggested.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Big Squeeze Quote  Post ReplyReply Direct Link To This Post Posted: October/28/2007 at 12:56
A good quality scope, should not have any change in POI from one magnification to the other. If so, send it back as defective and get another!!................
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RONK Quote  Post ReplyReply Direct Link To This Post Posted: October/28/2007 at 13:25

I've noticed a few posts in recent weeks in which someone will refer to a changing point of impact as he goes through the power changes. Reading between the lines, however, it becomes clear that he is referring to the changing reticle subtension in a SFP scope and the duplex-type reticle or ranging reticle he happens to be using. This is very misleading to the reader and it is not a true wandering zero situation. The bullet is still hitting the same place on target in angular  relation to the center crosshairs, but it looks different at different magnifications because the reticle size changes as you zoom the power up or down( in a SFP system.)

  I need to be more vigilant in beoitch-slapping such posters until they change their ways...

 

   

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Post Options Post Options   Thanks (0) Thanks(0)   Quote ND2000 Quote  Post ReplyReply Direct Link To This Post Posted: October/28/2007 at 14:03
Ronk -

I think I agree with everything you say until you mention the reticle size changes as you zoom in a SFP system.  I believe it's exactly the opposite.  In a SFP system, the recticle stays the same size, but APPEARS to change size because the target changes size as you change magnification.  In other words, in a SFP set-up the reticle will appear smaller at higher magnifications, because it covers less of the intended target.

FFP systems cover the same portion of the target regardless of magnification.

Someone please correct me if I've got this wrong.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote RifleDude Quote  Post ReplyReply Direct Link To This Post Posted: October/28/2007 at 16:26
Originally posted by RONK RONK wrote:

I've noticed a few posts in recent weeks in which someone will refer to a changing point of impact as he goes through the power changes. Reading between the lines, however, it becomes clear that he is referring to the changing reticle subtension in a SFP scope and the duplex-type reticle or ranging reticle he happens to be using. This is very misleading to the reader and it is not a true wandering zero situation. The bullet is still hitting the same place on target in angular  relation to the center crosshairs, but it looks different at different magnifications because the reticle size changes as you zoom the power up or down( in a SFP system.)

  I need to be more vigilant in beoitch-slapping such posters until they change their ways...

 

   

 

Hi, Ronk, it is technically possible for actual point of impact shift to occur during power change with a second focal plane reticle scope.  The reason for this is the reticle on a SFP scope is located in the zoom tube side of the erector assy near the eyepiece.  So, in some SFP scopes (mainly cheap scopes), as you rotate the power ring, thereby rotating the zoom tube, it can shift the position of the reticle very slightly, causing the POI to wander.  This happens because the zoom tube rotates around the reticle cell.  The degree to which this happens or whether it happens at all depends on how tightly fitted the internal parts of the scope are.  This is actually not that uncommon with cheap scopes.  In a first focal plane scope, this can't happen because the reticle is located on the objective end of the scope so that the zoom tube can't influence the reticle's position.

Ted


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Post Options Post Options   Thanks (0) Thanks(0)   Quote kphunter Quote  Post ReplyReply Direct Link To This Post Posted: October/28/2007 at 17:30

Ok, so with a Leupold VXI, do I need to worry about the reticle changing and affecting the POI?  I asked this question out of curiousity, not because I've actually experienced the issue before.

 

Thanks,

 

KP

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Post Options Post Options   Thanks (0) Thanks(0)   Quote RONK Quote  Post ReplyReply Direct Link To This Post Posted: October/28/2007 at 19:32

 ND2000- you are indeed correct. I should have made it more clear that I was referring to the reticle size as compared to the TARGET.

 

 Rifle Dude- Of course what you stated is true also, but it really shouldn't be noticible if the scope is of good construction. ( I'm not talking in terms of ABSOLUTE accuracy, either.)  I'm pretty sure the O.P. was referring to general "hunting" accuracy, within  perhaps half a Minute of Angle(?). So in the context of this thread, I really don't think the O.P. has to worry too much about it occurring. As mentioned by Technika, though, he should verify his scope by shooting it at different power settings to be sure.

  Regarding the posts of the last few weeks, those posters were referring to an SFP scope, the bullet hole in target as relating to the reticle's thick post or ranging hash marks at different magnification settings, and calling the comparison a P.O.I. change, when it was clearly not.

 I'm gonna hope that this clarifies my thoughts, but I am posting this with a headache and it really doesn't sound too good...Thanks for your contributions though, they always help me fine tune my posts.

 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote RifleDude Quote  Post ReplyReply Direct Link To This Post Posted: October/29/2007 at 07:04
Originally posted by RONK RONK wrote:

  Rifle Dude- Of course what you stated is true also, but it really shouldn't be noticible if the scope is of good construction. ( I'm not talking in terms of ABSOLUTE accuracy, either.)  I'm pretty sure the O.P. was referring to general "hunting" accuracy, within  perhaps half a Minute of Angle(?). So in the context of this thread, I really don't think the O.P. has to worry too much about it occurring.

 

Correct, with heavy emphasis on "scope is of good construction."  It all depends on how tight the mating tolerances of the moving parts in the scope are manufactured to, as well as how durable the scope is designed mechanically, both of which probably aren't characteristics of sub $150 scopes.  Most any high quality SFP scope shouldn't be a problem, but I guess anything is possible with anything as complex as a rifle scope.  One thing's for certain, the probability of it happening mechanically is infinitely greater with a SFP scope than a FFP scope, where it is highly unlikely.  I've recently seen 2 cheap scopes owned by a friend of mine of recent manufacture that had POI shift from just changing the power ring.  Both were BSA scopes, where the reticle actually rotated in the same direction of power ring rotation.  About 25 years ago, I had this happen with a brand new Leupold Vari-X II 3-9 on its first trip to the range, the only time I've ever tested their famous warranty.  Since then, I've seen at least 6 other scopes with this problem, all with retail price below $200.  In all cases, the amount of POI shift during power change was fairly significant -- at least 4MOA. 

Ted


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Post Options Post Options   Thanks (0) Thanks(0)   Quote cyborg Quote  Post ReplyReply Direct Link To This Post Posted: October/29/2007 at 09:42
Kp  I doubt you'll have a problem with it, it's a Leupold, pretty well known to be accurate throughout mag changes.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RONK Quote  Post ReplyReply Direct Link To This Post Posted: October/29/2007 at 18:56
Well, it IS a Leupold, but certainly not the company's top of the line model, either. I guess from all the well-rounded experience brought to this thread, we can probably all agree that the original poster would be wise to "trust, but verify...."
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Post Options Post Options   Thanks (0) Thanks(0)   Quote www.technika.nu Quote  Post ReplyReply Direct Link To This Post Posted: October/30/2007 at 00:33

There has been problems with Leuopld and shift, as well as problably every other manufacturer in the world of SFP optics.

There is only one way to find out and that is trying.

According to John Barnsness in his book Optics for hunters DEVA (German natinal test institution) did a test on a number of scopes. The tested Leupold WXlll 3,5-10 had a problem close to 1" at hundred meters.

 

Regards Technika

 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote cyborg Quote  Post ReplyReply Direct Link To This Post Posted: October/30/2007 at 07:01
Agreed You should always verify, several scopes are for hunting applications, so any poi change will likely still result in a kill. I have a Bushy Banner that I zeroed at the 24x and down to 6x at all mag changes there were no more than .75 inches from zero. surely as much as what you pay for a leupold that should be about the same. I also have 2 leupolds and neither give me any trouble at all, but they are a vxIII, and markIV, while I think Leupold is overpriced I can attest to their dependability. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RONK Quote  Post ReplyReply Direct Link To This Post Posted: October/30/2007 at 17:30
Originally posted by www.technika.nu www.technika.nu wrote:

There has been problems with Leuopld and shift, as well as problably every other manufacturer in the world of SFP optics.

There is only one way to find out and that is trying.

According to John Barnsness in his book Optics for hunters DEVA (German natinal test institution) did a test on a number of scopes. The tested Leupold WXlll 3,5-10 had a problem close to 1" at hundred meters.

 

Regards Technika

 

I don't doubt that, but again, I don't think that sub-  M.O.A  shift is going to be a problem for the Original Poster, unless he's going to be hunting lemmings or something...
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