POI Changing When Magnification Is Increased

[Brad93]

Scope is a Simmons ProAir 6-18 x 40. When the magnification is increased, the point of impact seems to drop by an ich or so, am I doing something wrong or is this a scope problem? It has taken a few knocks but seems (externally) fine

 

Thanks in anticipation

[Ozzy Fudd]

probably a scope problem, try to leave the magnification at a set amount

[SSS]

I use a hawke 3-9x50 on my .22lr and I leave it on 7x mag all the time. I have the same problem as you, so I zero on 7x and leave it.

[Dekers]

This should not happen, perhaps a trait of some less expensive internals on some scopes.

 

I have 7 different rifles and calibres, with a lot more different ammo, and a lot of different zeros, it's hard enough to keep track of what I'm carrying, let alone having to make additional calculations for different POI at changing magnification!

[Rem223]

Cheaper scopes are more likely to suffer from point of impact shift, but I have seen reviews where a range of scopes from bargain basement to very expensive models were tested and many of them were found to have this defect. It is actually quite difficult to engineer out poi shift. Hence cheaper scopes tend to suffer more. As stated above the simplest solution is to keep it at a fixed magnification or invest in a a better scope.

[Colster]

I've been wondering about this too although mine always stay on 6x but could it be down to the scope not being completely aligned with the barrel.

[Frenchieboy]

This could be a defect in the scope but as has been said already the POI shift through different magnifications can be very hard to manufacture out. I have experienced this on a couple of scopes, mainly the bigger magnification ones that go up to around X18 or X24 magnification, either raising or lowering the POI through different magnifications. Try zeroing it on one fixed magnification (Say something like X8 for instance) checking the zeroing at different ranges within your comfortable shooting zone and then keep it set to that magnification whenever you shoot. If this is not suitable for your style of shooting then the only option will unfortunately be to replace the scope.

[wymberley]

Hi,

Get some info on parallax error.

Cheers

[Dave-G]

Hi,

Get some info on parallax error.

Cheers

 

That may apply in some instances but consider the way the scope is built. It has an inner tube that can be manipulated to adjust the crosshairs. I'm guessing here but it's not hard to imagine that the only time the zero remains constant through the variable mag range is if the inner tube, and the retical, is completely central between the front and rear lenses.

 

If the inner tube is deflected elevation or windage wise - or both - the image of the retical will change position in the rear lense.

 

For the excercise, should someone wish to accept the mission, lol, I'd suggest mounting a camcorder to the rear lense - viewing though the scope at a target on record as the mag is adjusted though it's range.

[chrispti]

Second focal plane (sfp) scopes are more prone to zero shift when shooting on differant mag settings.

 

First focal plane (ffp) scopes do not, the zero stays the same at any mag