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Can Parallax Adjustment Greatly Affect Point of Impact at Various Ranges?

 
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Old 10-30-2007, 01:28 AM
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Can Parallax Adjustment Greatly Affect Point of Impact at Various Ranges?

My Weatherby Mark V Ultra Lightweight chambered in 300 Weatherby was a tack driver and with the very same load as I regularly shot .5 inch groups with at 100 yards recently shot as follows.

100 yards, great .5 inch group 3 inches high. I could cover the 6 shot group witha quarter.

I cleaned the barrel and went down to 300 yards. I adjusted the side paralax from 100 to 300 to accomdate the yardage change. I en started hitting 7-8 inches high where I then had to re sight in to be dead on at 100.

I went out again today adjusted paralax to 100 and from a clean barrel I was 3.5 inches high at 100 with sub par groups. I took it out to 300 adjsuted paralax to 300 yard setting and then shot 5 inches low at 300 where the previous day at the range I was dead on at 300 yards.

Have you ever heard of adjusting the parallax and it greatly affecting the point of impact at various ranges? I think something is messed up with my scope and this is the only variable I can think of besides shooting with swivel bipods.

What are your guys' thoughts on swivel bipods, my dad thinks it is the swivel bipods throwing everything off. I think it is something to do with my scope. It is a Zeis 4.5-14x44mm conquest never been biumped ever...

Thanks for your thoughts
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Old 10-30-2007, 06:25 AM
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FCH

If an optical instrument is imprecisely focused, the cross-hairs will appear to move with respect to the object focused on if one moves one's head horizontally in front of the eyepiece. This is why it is important, to carefully focus in order to 'eliminate the parallax', and to check by moving one's head.

Not sure if this is helpful to you.

I know on my scopes that have parallax adjustment they are not precise but I have not done enough testing at the longer ranges to determine how good or bad they are.
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Old 10-30-2007, 12:14 PM
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I have the same scope on my .338win, and like Mr. Hasketh just said, don't trust what the dial says. Sit down at the bench and play with the paralax untill the crosshairs stay put when you wiggle your head around, then make a note of where the dial was when it was set right.
The bipod could also be effecting POI if you are loading the bipod differently from group to group. Some rifles like a forward load some like a rear load and some like no load. Ya gotta get to know your setup and figure out what she likes. Was your cheek weld consistant from group to group? That could also be playing a factor.
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Old 10-30-2007, 01:42 PM
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Well, to start off, because you made a change in the parallax setting, does not necessarily mean that is the reason for other changes, so don't automatically over look other posibilities.

That being said.

Mostly, the calibrations on the parallax of a scope do NOT directly correspond the actual ranges.

This is something that you must test and verify. Then keep a cheat sheet for the adjustments on your regular tracking range notes.

Also... you must always adjust the parallax from the same direction, because the tracking forks have play in them. I can't speak to the Zeiss, but Leupolds must be adjusted from the larger distance to the shorter distance ALWAYS!!

That means if you want to go from 100 yds to 500 yds, you must go to the end (past infinity) then back to 500... if you want to go from 500 to 100, you can go directly from 500 to 100, but not the other way around.

For a Zeiss, you should test it and determine which direction the play comes into effect.


.
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Old 10-30-2007, 05:24 PM
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I think you're telling us everything was fine until you started using a 'swivel bipod' .....if so,

Quote:
Originally Posted by FullCurlHunter View Post
my dad thinks it is the swivel bipods throwing everything off. I think it is something to do with my scope.
Your dad is right.

[I'm quoting myself from an answer to a similar thread: http://www.longrangehunting.com/foru...0-yards-21560/ ]

Quote:
Originally Posted by Brown Dog View Post
Zane,

With strange POI changes I used to find myself guilty of a tendency to 'hear hoofbeats and think of zebras' ...rather than consider the simple solutions;

With what you've described, rather than equipment faults or ballistic weirdness, my first thought (having (far too slowly) trained my brain to 'hear hoofbeats and think of horses')relates to your consistency of 'position and hold' from occasion to occasion. For example:

-different surface under your bipod?
-leaning into the bipod for 1 group; but not the next?
-pulling the rifle into your shoulder for 1 group but not the next?
-differing cheek pressure on the stock etc............

All the best

Matt

Last edited by Brown Dog; 10-30-2007 at 05:27 PM.
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  #6  
Old 10-30-2007, 05:58 PM
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Quote:
Originally Posted by FullCurlHunter View Post
... I think something is messed up with my scope and this is the only variable I can think of besides shooting with swivel bipods.
...

How tall is your bipod? The taller the bipod the harder it is for me to stay consistent.

AJ
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