Scope shift

[horseman2]

A recent article question scope shift when changing power on a variable scope.
It was probably hiden within another post and since I only read the rimfire section, this is where it will start.

The rifle is a Cooper JSR model 57M with a Bushnell 4.5 -30 x 50. The ammo was Eley Match Biathlon with a published velocity of 1085.

Groups were 5-shots at 100 yards starting at 30 power and this group measured 0.91".
Second was shot at 8X and measured 0.81".
In the third group shot at 16X there was one low shot and the measurement was 1.20".
Back to 30X and the group was 0.92".

There was no appreciable change in the point of impact.

This is fairly consistent with one of the challenges where the maximum power was 12.
My first group was shot at High power and then scaled back to 12.
Two of the three groups at 12 power were better were better than the maximum setting.

 

[Longstud]

Do you think it could possibly be more parallax related? Those are all great groups for 100 yards and could be just the conditions in which they were shot. As far as the one flyer, Id chalk that up too rimfire ammo. Was there any mirage at the higher magnifications?

 

[horseman2]

From the article I referred to, I would be inclined to think their issues might have more parallax related isues.
It is more likely to occur in variable scopes without a side focus or an adjustable objective.
The conditions last night were absolute calm, about 14 degrees.

 

[grauhanen]

"Scope shift"? I must admit it's not clear to me what the question or issue is about.

Is it about group sizes relative to scope magnification or something else?

A recent article question scope shift when changing power on a variable scope.
It was probably hiden within another post and since I only read the rimfire section, this is where it will start.

From the article I referred to...

Is it an article referred to here (originally published elsewhere) or a CGN member's post?

 

[horseman2]

"Scope shift"? I must admit it's not clear to me what the question or issue is about.

Is it about group sizes relative to scope magnification or something else?

Is it an article referred to here (originally published elsewhere) or a CGN member's post?

No recall where I read it but the suggestion related to significant change in impact with different magnification changes.
The time it took between reading the article and performing some tests when conditions were excellent was two weeks to a month.
The rifle/scope combination was one with 4.5 - 30 power variation.
With my various scopes on rimfire rifles the maximum power would be selected as it helps to determine when there are two shots in one hole.
My normal hunting with variable scopes was never really tested. Finding a grouses head at 10 yards at low power was never an issue and shift in POI never entered my thoughts.
At lower power, Parallax was eliminated at close range.
The discussion might be more applicable in Centerfire/hunting scenario where parallax adjustment does not normally exist.
Reading the article prompted my interest and the discussion started from there.

 

[grauhanen]

Regardless whether the reference is to an article or a post (they're not the same), it's still not clear what the issue is about. Is there reason to believe that changing the magnification of a scope will change the POI?

 

[Longstud]

Regardless whether the reference is to an article or a post (they're not the same), it's still not clear what the issue is about. Is there reason to believe that changing the magnification of a scope will change the POI?

Read the first line in the original post by horseman2. Seems pretty evident what the subjects about. Too bad you dont catch on as quick as your sarcasm spews forth. Only problem with blocking is ,still see the culprit when reply with qoute is used.

 

[grauhanen]

Read the first line in the original post by horseman2. Seems pretty evident what the subjects about. Too bad you dont catch on as quick as your sarcasm spews forth. Only problem with blocking is ,still see the culprit when reply with qoute is used.

Mr. Long Stud, more than a month has gone by since the last time you responded to anything I've said. For a question that seems to you to be self evident, however, you choose to be small-minded rather than offer your relevant ideas -- if you have any. While you appear to be scarred by your experiences, the pettiness is tiresome. As I urged previously, please use the ignore feature. It may help as you as try to recover from whatever ails you.

 

[Alpheus]

I think this issue of shifting point of impact with changes in magnification are more to do with older scopes, with the moving lenses within a variable power scope not staying perfectly concentric and aligned with the reticle. As manufacturing and QA processes have improved, I think the problem has largely gone away (cheap chinese junk notwithstanding). Granted, I've never specifically tested for this, but I can't think of any instances, first or second hand, where this might have occurred.