Change in POI when zooming

[Gambler]

Hi. I bought a used NcStar Mark3 10-40x50 scope and trying to zero it in on 40m.
I started with 18x and hit low, I turned the knob "up" and had to turn all the way to the point it didnt go any higher and hit low 3 and 4 (red mark) but when I zoom in to 30x i hit black (blue mark) without adjusting the knob. I dont mind shooting with 30x zoom but utstyr hard to find targets at closer range. It looks like if I zoom out to 28x i might hit center tho, but this cant be right?

 

[Sqwirl57]

POI shift while zooming is a common issue with budget optics. You either need to learn to work with it or get something better unfortunately

 

[nervoustrig]

Correct, the scope’s POA should not change with the magnification. There’s an outside chance parallax error is contributing to the result above...those groupings tell me it’s unlikely but not zero. To prove it’s the scope’s fault, clamp it to a rigid, unmoving object (e.g. heavy table). Set its magnification to the maximum and focus it on a grid or similar target downrange. Make sure your eye is centered by backing away until the haze around the perimeter is centered. Note where the crosshair lies against the grid/target.

Then back the magnification down to a lower value and repeat checking where the crosshair is on the target. Is it a different place?

Return to max magnification and check that the crosshair returns to the original spot. This step is a sanity check to confirm the scope is repeatable at a given magnification and that your table/clamping approach isn’t moving.

 

[Firewalker]

First focal plane solves this phenomenon, second focal plane leaves the reticle the same size and you have to dope your yardage.

I dope X27 and again at X10 on my Alpha 6.

 

[Slingworks]

That's a possibility in any rifle scope. When you buy a cheap scope it's almost a given. Your scope probably doesn't track well either.

I really prefer fixed magnification glass as it eliminates allot of issues and are generally brighter as well.

Yeah, it's allot harder to find a good fixed 4, 8, 10 or 12x glass these days.....

As much as I hate variable x glass, I did install a "vintage" Nikon Prostaff 3-9x40 on my Caiman 25. The glass on it is excellent for what I'd consider a budget scope. No tracking issues or POI shift. You probably wouldn't like the duplex reticle though.... They're pretty cheap and easy to find if you look around. Parallax is set at 100yds, but you can adjust it if you know what your'e doing. (I used to repair glass).

 

[Gambler]

Maybe i Just put my BSA 4.5-14x44mm FFP back on again then

 

[.20calguy]

POI shift while zooming is a common issue with budget optics. You either need to learn to work with it or get something better unfortunately

Oh oh Lol

 

[.20calguy]

Maybe i Just put my BSA 4.5-14x44mm FFP back on again then

My two variable hi power scopes are a NcStar, and a BSA. Lol
I haven’t had either one on a gun that shot well enough to test the scopes accuracy.

 

[Sqwirl57]

Maybe i Just put my BSA 4.5-14x44mm FFP back on again then

That may not be necessary. Are you using the scope for Field Target by chance? How far was that group in your original post shot at?

 

[Hateful McNasty]

Theres a 3 part test thing at p.a blog. Using pcp and springer ..

https://www.pyramydair.com/blog/2015/09/poi-shift-when-changing-the-scopes-power/

Maybe find somthing in it?

 

[nervoustrig]

Theres a 3 part test thing at p.a blog. Using pcp and springer ..

https://www.pyramydair.com/blog/2015/09/poi-shift-when-changing-the-scopes-power/

I guess it wasn’t obvious when Tom set out to do the test...no need to do any shooting at all. No need to introduce the variables of the gun’s accuracy, wind influence, etc. Could have tested the scope in 5 minutes by clamping it to a table and wind up with a more confident verdict.

 

[Hateful McNasty]

I guess it wasn’t obvious when Tom set out to do the test...no need to do any shooting at all. No need to introduce the variables of the gun’s accuracy, wind influence, etc. Could have tested the scope in 5 minutes by clamping it to a table and wind up with a more confident verdict.

Yup, the solid mounted tracking test tells all..

 

[AirShot]

Most all scope mfgrs tell you to never crank the reticule knobs all the way in any one direction as it can damage the erector system. Especially on cheaper scopes, have saw many ruined from doing this and it can also void any warranty you might have.

 

[Gambler]

That may not be necessary. Are you using the scope for Field Target by chance? How far was that group in your original post shot at?

Yeah field target, 40meter is the pic i posted.

 

[Sqwirl57]

Yeah field target, 40meter is the pic i posted.

Piece of cake then. Range at 40x and shoot at a whichever magnification you're most comfortable with and stick with it. Personally I just stick to high magnification unless its windy and need to pick up on ques down range.

The other option is to just know the difference between max and whatever magnification you're currently shooting. Its usually a pretty consistent shift. In that pic I would assume 2 MOA needs to be adjusted in but you'll need to verify that for yourself

 

[Xbowsniper]

For a second Focal Plane scope, the point of impact will APPEAR to change when magnification is changed, but the impact will not. Follow this example, for instance.
You have a 10-50 power scope.
The scope is zeroed at 30 yards (a very typical FT zero distance).
You shoot at 30 yards at ANY magnification, the projectile should hit at the same point. If it does not, the scope is surely damaged.
Also, if turrets are bottomed out, damage can be bestowed on the scope. The easiest solution is to use adjustable scope mounts to alleviate the problem. The scope must be returned to optical zero, before resighting process continues.
Shoot at 55 yards at 30 x. Aim at the middle of target. The point of impact will be around 3 inches lower (depending upon power and/or projectile. Let's say around 800 FPS for an 8.4 grain pellet. That would make 3 inches realistic)
If you look through your scope, at 30 X, it might be 1-1.5 mil dots low. The projectile is around 3 inches low.
Now, set your scope to 50 X, and shoot at the center again. Your projectile will (or should) go into the same spot as the one shot at 30 X. Look through your scope. Now instead of 1.5 mildots, it will be much less, maybe not even .5 a mildot.
Thus the virtues of a Second Focal Plane scope. A First Focal Plane scope should hit ANY and ALL mildot holdovers at all magnification settings. If it does not, it could be damaged.
Always keep in mind, all scopes should be zeroed at the highest magnification. When turned down, they should hold zero. If not, the scope is damaged.
Never sight in a scope at a lower, or mid magnification of the scopes capabilities. This will only magnify the error, no matter how slight it is. This applies to both First and Second Focal Plane scopes.
Hope some of this helps.

Tom Holland
Field Target Tech
Fieldtargettech.com

 

[c_m_shooter]

Your center zero should not change with magnification. If it does, you have a bad scope. If you are using the Mil Dots or ballistic reticle for holdovers with a second focal plane scope, they will only be accurate at one power level.

 

[JimNM]

The Point of Impact does not ever change for any reason due to scope, any scope expensive or cheap, FFP or SFP. POI is determined solely and completely by ballistics. Lock the gun into a vise and test POI with the scope on. Then take the scope off....and Poi has not changed. Ergo, POI is not influenced one bit by the scope.

Point of Aim is a visual issue, and Point of Aim is completely dependant on the scope.

I try to be accurate with my gun, and my language.

 

[Sqwirl57]

You guys are taking things a bit too literally and really doesn't help OP at all. If you aim at the same spot and the pellet is impacting two different places at two different zoom levels, the point of impact is absolutely changing. The POA is still the exact same (as far as the shooter can tell) hence the issue OP is having here. This isn't an uncommon issue with lower end scopes or even some more expensive ones.

 

[nervoustrig]

Yeah I can see both perspectives. Back in reply 3 I applied the term POA

the scope’s POA should not change with the magnification.

... in the interest of using the correct terminology, but being aware that a predictable POI is what we care about, it’s understandable that people will describe it as a POI shift.