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All Springer/NP/PCP Air Gun Discussion General > Optics, Range estimation & related subjects

Optimal scope setup

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Motorhead:
Been prowling the web and found this site ... Airguns too !!
Has a VERY IN-DEPTH analysis on height & cant there as well.
Very much worth a read IMO.

SEE: http://www.szottesfold.co.uk/2012/03/high-scope-and-canting-end-of-ancient.html

Scott S

whitefox545:
Scott,  Read this about a year ago and it seems like it disproves the old story about cant being worse when scope is mounted high, I have shown it to many high quality shooters (some of which were snipers in the service) and they would not con seed to the theory.  I can honestly say that I have not see ant difference when having my scope mounted higher than when it was mounted lower. I can say that canting of any amount no mater what the scope height will cause a change in POI that is for certain so I have to kinda go along with the explanation.  Whats your thoughts as you have been at this a lot longer than me?   J.L. 

nervoustrigger:
Yeah this was a common misconception I held for a long time until I did this little hypothetical scenario...

Imagine a rifle with two scopes installed, one above the other.  Zero them both to 25 yards.  The distance doesn't matter...all we care is that the crosshairs for each scope intersect the trajectory at the same distance.  If the crosshairs intersect at the same distance, so do their mildots lie on top of each other. 

That's it, that's all that matters.

If that doesn't quite click in your mind, think of cant error as how much your point of aim is off by virtue of tilting the rifle.  Or in other words, by how much the pellet misses your intended point of aim, your point of aim being some mildot.  If the mildots for both scopes lie on top of each other, then their errors are the same.

bandg:

--- Quote from: whitefox545 on November 27, 2018, 09:29:54 AM ---Scott,  Read this about a year ago and it seems like it disproves the old story about cant being worse when scope is mounted high, I have shown it to many high quality shooters (some of which were snipers in the service) and they would not con seed to the theory.  I can honestly say that I have not see ant difference when having my scope mounted higher than when it was mounted lower. I can say that canting of any amount no mater what the scope height will cause a change in POI that is for certain so I have to kinda go along with the explanation.  Whats your thoughts as you have been at this a lot longer than me?   J.L.

--- End quote ---

I can't understand what you are saying above about the "high quality shooters" or "snipers in the service".  Are you saying that they DO BELIEVE that higher mounting makes cant errors worse or DO NOT BELIEVE that?

I don't believe that the mil dot example is correct.  If one scope is mounted above the other then LOS for the higher scope would have to be angled slightly more downward IN RELATION TO THE BORE in order to hit the point of aim than would LOS for the lower scope.  It is different.  Small difference but different.

My way of visualizing this-
Consider X scope mounted 1 inch above bore and Y scope mounted 2 inches above bore, both zeroed at 30 yards.  Tilt rifle 45 degrees clockwise (crosshairs still on aim point but muzzle has now moved left of vertical).  X muzzle is now 1 inch low and left along a 45 degree line while Y muzzle is now 2 inches low and left along same 45 degree line.  Different related to mounting height.  At 15 yards X point of impact is 1/2 inch low/left along 45 degree line while Y point of impact is 1 inch low/left along same 45 degree line.  Both hit point of aim at 30 yard zero.  At 45 yards X impacts 1/2 inch right while Y impacts 1 inch right.  At 500 yards these distances become roughly 15 inches for X and 30 inches for Y.  Depends on target size but one would likely produce a hit on a 20 inch target while the other would miss.  Scope height does effect cant error.  It seems to be a small difference but it certainly appears to be different. 

The difference becomes progressively larger at longer distances but the cant error itself seems to be more important than the difference in mounting height.  There was a statement posted recently about military concept being 6 degrees of cant producing 55 inches of error at 1000 yards.  That would be for ONE specific mounting height.  Change that mounting height and that error amount would change, albeit probably very slightly.  Seems that the cant itself is the primary producer of the error but mounting height has to be a factor.

nervoustrigger:

--- Quote from: bandg on November 27, 2018, 02:42:34 PM ---
If one scope is mounted above the other then LOS for the higher scope would have to be angled slightly more downward IN RELATION TO THE BORE in order to hit the point of aim than would LOS for the lower scope. 
--- End quote ---

What you say there is true...the higher a scope is mounted above the bore, the more it will need to be angled downward to intersect with the pellet's trajectory.  However that has no influence on cant error.  However you zero the two scopes, whether it's by way of moving their erector tubes (turrets) or by way of angling the scope tubes (e.g. adjustable rings), their mildots lie on top of each other.

You can however make the case, if taken to a really ridiculous extreme, they will begin to deviate.  For example, consider one scope mounted as close to the bore as possible and the other 100 feet above the bore.  Now the high scope is appreciably further from the target (hypotenuse of the triangle formed by the target relative to the two scopes).  But for practical examples where a scope is somewhere between 1.5" - 2.5" above the bore, there's no difference.


--- Quote from: bandg on November 27, 2018, 02:42:34 PM ---
My way of visualizing this-
Consider X scope mounted 1 inch above bore and Y scope mounted 2 inches above bore, both zeroed at 30 yards.  Tilt rifle 45 degrees clockwise (crosshairs still on aim point but muzzle has now moved left of vertical).  X muzzle is now 1 inch low and left along a 45 degree line while Y muzzle is now 2 inches low and left along same 45 degree line.  Different related to mounting height.  At 15 yards X point of impact is 1/2 inch low/left along 45 degree line while Y point of impact is 1 inch low/left along same 45 degree line.  Both hit point of aim at 30 yard zero.  At 45 yards X impacts 1/2 inch right while Y impacts 1 inch right.  At 500 yards these distances become roughly 15 inches for X and 30 inches for Y.  Depends on target size but one would likely produce a hit on a 20 inch target while the other would miss.  Scope height does effect cant error.  It seems to be a small difference but it certainly appears to be different. 

The difference becomes progressively larger at longer distances but the cant error itself seems to be more important than the difference in mounting height.  There was a statement posted recently about military concept being 6 degrees of cant producing 55 inches of error at 1000 yards.  That would be for ONE specific mounting height.  Change that mounting height and that error amount would change, albeit probably very slightly.  Seems that the cant itself is the primary producer of the error but mounting height has to be a factor.
--- End quote ---

That way of reasoning it out seems very similar to the same one I used to erroneously use.  That is, I thought okay, if I tilt the rifle something absurd like 45 degrees to the left, obviously a scope that is higher will now be sitting out further to the left than one which is closer to the bore.  However the POI error would only be worse if its reticle were not oriented correctly so it intersects the barrel.  That's not a fault of canting the rifle, that's a fault of the scope being installed incorrectly.  Granted both are common errors and must be taken into account, but they are indeed different things.

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