GTA
All Springer/NP/PCP Air Gun Discussion General => Air Gun Gate => Optics, Range estimation & related subjects => Topic started by: Motorhead on November 27, 2018, 01:29:15 AM
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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 (http://www.szottesfold.co.uk/2012/03/high-scope-and-canting-end-of-ancient.html)
Scott S
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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.
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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.
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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.
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.
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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.
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.
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.
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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Yes the 45 degree angle is extreme to make a point. And your scenario is stated as a hypothetical as well. But I don't see how you can argue the physical situation I laid out. It doesn't matter that the 45 degrees is extreme and no one would shoot that way. It does matter that it illustrates that different mounting heights will have a different point of impact with the same amount of cant. Assume 6 degrees of cant which would still seem to be an amount most could see. There would still be a difference, even if small, due to mounting height. And I still don't agree with your view on the mil dots. Yes they would be roughly aligned with each other but not similarly with the bore. They would both converge on the bore and would have to do so at different rates. I'll still believe that mounting height will have an effect on cant error. That difference will be much more for longer ranges but is there at any distance other than the zero distance. But the cant itself is the thing to focus on.
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I don't see how you can argue the physical situation I laid out. It doesn't matter that the 45 degrees is extreme and no one would shoot that way. It does matter that it illustrates that different mounting heights will have a different point of impact with the same amount of cant.
The physical situation you laid out is correct insofar as a higher scope will swing further from the 12 o'clock position, but the resulting cant error is only greater if the scope is also misaligned to the bore. It's simply a different source of error. Important, yes, but different and distinctly unrelated to how much the gun is being canted.
I still don't agree with your view on the mil dots. Yes they would be roughly aligned with each other but not similarly with the bore. They would both converge on the bore and would have to do so at different rates. I'll still believe that mounting height will have an effect on cant error.
Trust me, I know this is hard to sort out. You are falling prey to the same geometric fallacies I was.
You agree that the mildots are roughly aligned to each other. I will disagree with the roughly part...by way of the hypotenuse qualification I made earlier, there is indeed some difference in how precisely the two sets of mildots lie on top of each other but unless we separate the scopes vertically by a completely unusable amount, that difference is completely academic.
So ask yourself this, what is cant error if not "I was aiming here, but I had the rifle tilted so it actually hit there? So if the mildot in each scope was on top of the point here when you pulled the trigger, the errors are the same and there is no difference between the two scopes.
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As simple as I originally noted-consider the two different height mounts "correctly mounted" and zeroed at ANY distance. Then consider the rifle tilted at some angle (45 degrees for easy visualization but ANY angle). Cross hairs stay on aim point and muzzle shifts out to the side. Shots will hit at the same point at only one place, the zero distance. They will hit at different points from the muzzle to the zero distance with the difference decreasing as they approach the zero distance when they will both hit point of aim. Beyond that set zero distance they will again hit AT DIFFERENT POINTS with the difference increasing as long as the range increases. If you can think of any way for anyone to verify what you claim then describe it. Anyone can go to their back yard, "correctly" mount a scope with low mounts and then with high mounts, fire shots at a consistent amount of cant, and OBSERVE the change for themselves.
Think of it more simply if it helps you understand-do the two different mounting heights hit at the same point from muzzle to zero and beyond even if "correctly mounted" and held perfectly level? No, they do not. They only hit at the same point at the zero distance. The taller mount will hit more below the line of sight at/near the muzzle. Surely you've heard discussions of holdover needing to be greater at very close ranges to hit a target with tall mounts in relation to low mounts. It's the same thing. Cant the rifle (remember you cannot cant a mounted rifle/scope setup independently as they are mounted rigidly together and "incorrectly mounted" has nothing to do with this) and the point of impact moves to the side along the same angle but the taller mount moves that POI slightly more to the side (it is a longer radius from bore to scope). It is not the same.
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Anyone can go to their back yard, "correctly" mount a scope with low mounts and then with high mounts, fire shots at a consistent amount of cant, and OBSERVE the change for themselves.
Not so, and that statement runs counter to the well documented article that Scott posted at the beginning of the thread.
Think of it more simply if it helps you understand-do the two different mounting heights hit at the same point from muzzle to zero and beyond even if "correctly mounted" and held perfectly level? No, they do not.
No, but again that is unrelated to cant. The difference you are referring to is one that affects elevation. Cant is predominantly an error of windage.
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"No, but again that is unrelated to cant". Nonsense. It is directly related to cant since the scope is rigidly mounted to the rifle. The radius is shorter for lower mounts than for taller mounts. Simply draw it out to see.
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I have drawn it out, multiple times in fact as I grappled with it over the years.
Are you contending that the author of the article is wrong?
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...They only hit at the same point at the zero distance....
That's a good place to start. Realize that and the rest will follow:
You need to realize that in most situations, most of us are always at our "zero" when we take the shot.
Normally, when aiming for a target, we re-zero. Either by clicking to re-zero the crosshair, or by choosing a different mil-dot or stadia point as the new zero. In both cases, the scope has been "re-zeroed" for that distance. The POA (Point Of Aim) and the intended POI (Point of Impact) coincide. Any cant is pivoting about the intended POI. So scope height will not affect the amount of error from canting the gun.
A less common method that does not involve a re-zero is to aim at a point above the intended POI. In that case, the POA and the intended POI do not coincide. Any cant is pivoting about the POA. The more "holdover" required, the greater the cant error.
We can call the use of mil-dots as "virtual holdover" and the use of a different aim point as "physical holdover".
Virtual holdover (i.e.- using mil-dots or stadia marks as the zero points)- scope height will not affect the amount of cant error. Cant error is determined by amount of drop, which is the same regardless of scope height.
Physical holdover (i.e. - aim for the head to hit the body) - scope height will affect the amount of cant error. Cant error is determined by the amount of correction required, which is more for high scopes at close distances and less at far distances.
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Very diplomatically stated.
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Bear with me here for a minute.... Let's sight our rifle in for 100 yards.... and ignore wind drift and the spin drift of the projectile.... The scope is installed with no cant in relationship to the barrel, ie the vertical crosshair of the scope passes through the barrel C/L.... Let's pick a bullet (960 fps, BC=0.2) which has 20" of drop in 100 yards.... The higher the scope is mounted above the bore, the less the bullet will appear to rise above the POA, however, even though it's trajectory is unchanged.... Check this with Chairgun if you don't believe me.... Use the above BC and velocity, and scope heights of 1.5" and 11.5".... Turn on the "Bore Line" (under "Embellishments") in Chairgun, and set the maximum range to 200 yards, with the gun sighted at 100 yards.... With the scope height of 1.5", the boreline is 1.5" below the LOS at the muzzle, and 41" above the LOS at 200 yards.... However, with the scope height of 11.5", the boreline is 11.5" below the LOS at the muzzle, and 51" above the LOS at 200 yards.... However, in both cases, the boreline is 20" above the LOS at 100 yards (the bullet drop at that distance)
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Now, lay the rifle on it's right side, ie 90 deg. of cant, with the scope to the right of the barrel.... The horizontal crosshair is now vertical, and the vertical one is horizontal.... Where would the bullet hit, relative to the POA (where the crosshairs intersect)?.... Since you were sighted dead on at 100 yards to start, the boreline is pointing up, at 20" in 100 yards, to the (originally) horizontal crosshair, but aligned with the vertical crosshair, but since the pull of gravity remains vertical, and the horizontal crosshair is now vertical, the bullet hits 20" to the right of the POA.... In addition, since the barrel was aligned with the vertical crosshair, but that crosshair is now horizontal, gravity is pulling the bullet "down", and the bullet hits 20 MOA below the POA.... So when you lay the gun on it's side, the bullet hits 20" to the right and 20" low, compared to the POA.... This should hold true AT 100 YARDS, regardless of the scope height above the barrel, because the trajectory and the POA intersected at 100 yards.... This applies to scope cant AT THE POA.... Scope height makes no difference to cant error at the distance the gun is sighted in....
When you are shooting at some intermediate distance.... or at some distance past the POA.... things change, and the scope height DOES make a difference.... This is because that even though the rifle is sighted in at 100 yards, at less than that distance, the bullet rises less above the LOS with a high mounted scope, and also falls less from the LOS at longer ranges.... Let's examine the 2 cases....
With the scope 1.5" above the bore, at 50 yards the boreline is 9" above the LOS, and at 200 yards it is 41" above.... Lay the gun on it's right side, and the bullet will hit 9" to the right at 50 yards, 20" at 100 yards, and 41" at 200 yards....
However, with the scope 11.5" above the bore, at 50 yards the boreline is only 4" above the LOS, and at 200 yards it is 51" above.... Lay the gun on it's right side, and the bullet will hit 4" to the right at 50 yards, 20" at 100 yards, and 51" at 200 yards.... A higher scope has less horizontal cant error closer than the sighted distance, but more horizontal cant error further away....
What about the vertical error, does that change with scope height?.... Well, no it doesn't, because the trajectory doesn't change when you change the scope height.... The boreline was exactly aligned with the vertical crosshair when the gun was sighted at 100 yards.... The drop of this bullet is 4.9" at 50 yards, 20" at 100 yards, and 84.2" at 200 yards.... Since the vertical crosshair is now laying horizontal, the boreline is now also horizontal, relative to the POA.... Therefore it will hit 4.9" low at 50 yards, 20" low at 100 yards, and 84.2" low at 200 yards, regardless of the scope height.... Scope height makes no difference to the vertical cant error, regardless of distance....
I realize that I have chosen a ridiculous amount of cant to show what happens.... but the actual cant error will be a sine or 1-cosine function, depending on the angle of cant, times the type of calculations done above.... Cant error has two components, one vertical and the other horizontal.... The horizontal distance you "miss" is affected (slightly) by the scope height.... but the vertical distance you "miss" is not.... For small angles of cant, the vertical change in the POI, relative to the POA, is small, and can probably be ignored.... In the above example at 200 yards a 10 deg. cant (which is a lot) would only change the vertical POA by 1.3", and at 50 yards only by 0.074", regardless of scope height.... However, with a 1.5" scope height, the horizontal error would be 7.11".... while with a 3.0" scope height it would be 7.38".... At 50 yards (sighted at 100) the horizontal error with a 1.5" high scope would be 1.56".... while with a 3.0" scope height it would be 0.69"....
The horizontal cant error is TWICE the above numbers, however, if you are using holdover.... Using the above example, at 200 yards the holdover is 41".... If you cant the rifle 10 deg. to the right, and hold 41" high by using Dots on the vertical reticle (the normal method), your aim point is going to be rotated to the left of the point where the crosshairs intersect by 7.11".... This is in addition to the boreline being tilted 10 deg. to the right, which would cause the bullet to land 7.11" to the right of the crosshair intersection at 200 yards.... Therefore, the bullet will hit over 14" to the right of the Dot you are using to aim.... Note that "clicking in" an elevation correction doesn't improve the situation.... By the time you clicked in 41" (~ 20 MOA) of vertical to get back on target at 200 yards, the boreline is now 84" above the POA, and you are right back to that over 14" of horizontal error at 10 deg. of cant....
Bottom line is.... align the vertical reticle with the bore when mounting the scope.... and then hold the crosshairs level when shooting....
Bob
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Bottom line is.... align the vertical reticle with the bore when mounting the scope.... and then hold the crosshairs level when shooting....
Bob
And avoid aiming high. Instead, click or use your mil-dots/stadia as holdover aim points. Your aim point should be the bullseye, not some other point. If you do that, scope height won't be a additional contributor to inadvertent cant errors.
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Sorry, but how is "use your mil-dots/stadia as holdover aim points" different from "aiming high"?
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Sorry, but how is "use your mil-dots/stadia as holdover aim points" different from "aiming high"?
(http://www.scotthull.us/photos/Misc/aim-point-00.jpg)
(http://www.scotthull.us/photos/Misc/aim-point-01.jpg)
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Agree with most of the rsterne post 13 above but not all.
"A higher scope has less horizontal cant error closer than the sighted distance but more horizontal cant error further away". Second part exactly right, first part dead wrong. Think simply of your example of 1.5 inch height and 11.5 inch height (scope above bore). Tilt both (either left/counterclockwise or right/clockwise) the same amount. You really think the bore under the higher mount would be closer to the vertical than the bore under the lower mount? If so, make a simple diagram and you will see you are wrong. The bore would be further from the vertical with the higher mount and that is CANT ERROR. For anyone wanting to simply see this, take a string and make a mark at 1.5" and 11.5" from the end. Now tilt the string. The end of the string is LOS and the mark is the bore. Which mark is further from the vertical?
"Scope height makes no difference to vertical cant error, regardless of distance". Wrong. Simply consider again your 1.5" and 11.5" mounting heights zeroed at 100 yards. Cant both the same amount. 10 yards from the muzzle the 11.5" mount will impact WELL LOW in relation to the 1.5" mount and WELL LEFT or RIGHT (depending on cant direction). The vertical difference in point of impact between the two will decrease with distance as they approach zero distance. "Regardless of distance" is simply not accurate. Your assertion may well match at and beyond the zero distance but I am not certain.
This is a pretty good article with some relevant diagrams related to these concepts. www.riflescopelevel.com/cant_errors.html (http://www.riflescopelevel.com/cant_errors.html)
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Sorry, but how is "use your mil-dots/stadia as holdover aim points" different from "aiming high"?
(http://www.scotthull.us/photos/Misc/aim-point-00.jpg)
(http://www.scotthull.us/photos/Misc/aim-point-01.jpg)
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Sorry but when I try to quote these posts it puts my comments in as part of your post. I see what you are saying-assuming the rifle is canted. But how about aim high but don't cant. :D
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bandg
. I suggest you go back and read the article linked in the OP.... Pay attention to Chapter 3 "When a High Scope is Worse", and Chapter 4 "When a High Scope is Better".... My statement exactly agrees with those two chapters.... Go to ChairGun and input the data, and you will see for yourself....
There is no difference in the cant error between a high and low scope AT the range you are zeroed, but there will be a slight difference at all other distances.... The article you linked says that any cant past 5 deg. is likely to be noticed and corrected by the shooter, and I would agree with that.... This means that the vertical cant error is very small, and the difference between a high and low scope even smaller.... In fact, at 5 deg. of cant, the vertical cant error is less than 0.4% of the total drop below the boreline, because (1-cos5) = 0.0038.... That is NOT the case with the horizontal cant error, which is what we are really concerned with....
I think your confusion about the vertical cant error is because the vertical POI is already different with a high scope.... You are correct that at 10 yards the impact with the 11.5" high scope will be well low, compared to the 1.5" scope.... but that is already the case, even with no cant.... The VERTICAL CANT ERROR does not change with scope height.... but the HORIZONTAL one certainly does....
Bob
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There is no difference in the cant error between a high and low scope AT the range you are zeroed, but there will be a slight difference at all other distances....
When POA matches the intended POI, than scope height NEVER matters with regards to gun cant. Not even a slight difference.
What do you mean by "AT the range you are zeroed"?
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"AT the range you are zeroed" means exactly what you said.... POA matches POI when your target distance IS the same as your zero distance, so scope height doesn't matter.... However, if you are sighted at a given distance, and shooting either closer or further away, the scope height can make a slight difference to the cant error.... just as it makes a difference to the POI distance above or below the LOS/POA....
We are agreeing with each other, Scott....
Bob
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".... However, if you are sighted at a given distance, and shooting either closer or further away, the scope height can make a slight difference to the cant error...."
Ok. Agreed. Ranging errors will add another variable .
If the distance is different than our zero, than what we actually have is a range finding error, which results in a holdover error, which varies with scope height. If it is also canted, those errors are canted.
If all we have is gun cant error (no range finding error), scope height does not affect it. Hopefully, we all agree on that.
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If I recall correctly, in that same article (possibly it was another article related to "vertical cant error" search but I don't think so), the writer stated that he noted horizontal errors as expected but was surprised that the vertical error was much higher than he thought it would be in relation to cant. Personally, I've always thought of cant error only in terms of the horizontal movement since I considered it a greater effect on accuracy than the vertical component but maybe I should put more weight on the vertical part as well.
I think in general we are all in agreement but not sure. I use holdover but also use mechanical levels so I should not have to consider the effect of cant vs. holdover. The levels eliminate the cant and any holdover I use should therefore be in the vertical plane.
I also had trouble with this statement in reply #13-"a higher scope has less horizontal cant error closer than the sighted difference". That is just wrong. I'll simply go back to the basic mechanics. Forget ranging for a second. Consider rsternes 1.5" vs 11.5" inch mounting heights in his original post. Now cant the rifle the same amount for each height around the scope centerline as anyone would do firing a shot at zero distance. Crosshairs on target but muzzle laterally moved to the side. Classic cant error-aiming where you want to hit but rifle canted. It is IMPOSSIBLE for the higher mount condition to not move the muzzle more laterally than the lower mount for any given amount of cant. Simple geometry (the longer radius) and mechanics (the scope is bolted rigidly to the rifle). Cant the rifle any amount and a higher mounted scope will cause the bore to shift more laterally than will a lower mounted scope. MORE horizontal cant error closer than zero distance, not LESS. The radius from scope bore (LOS, point of aim)to muzzle is longer for the higher mount thus the muzzle will move slightly more laterally caused only by the relative height of the scope mount in this situation. Thus a higher mount will cause slightly MORE cant error at any range closer than zero range than will a lower mount. Beyond zero range the error will also be greater for a higher mounted scope and will gradually increase due to continued divergence of flight path from vertical until the projectile stops. MORE error at longer ranges and progressively MORE error for higher mounts at longer ranges with any amount of cant.
This amount of closer than zero distance horizontal error would be small for either height. But it is physically there and would be greater for a higher mounted scope than for a lower mounted scope. It would probably be notable only in a situation where someone was zeroed at maybe 30 yards and shooting at a target at 10 yards. You would have to hold over to hit the closer target (as normal) but 5 degrees of cant would move the POI laterally a small amount as well. Enough to cause a miss? Probably not but it depends on how small the target is and how high the scope is mounted.
As Scott said before, mount scope correctly (level to bore) and hold it level when you shoot. And the hold it level part seems especially important if you use holdover.
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Personally, I've always thought of cant error only in terms of the horizontal movement since I considered it a greater effect on accuracy than the vertical component...
I agree, and it's pretty easy to see that in Perry Babin's animation here http://www.arld1.com/impactpointvscantangle.html (http://www.arld1.com/impactpointvscantangle.html)
Swing the rifle just a few degrees and you can see the POI shifts much more to the side than it does vertically. As you continue to increase the cant to unrealistic levels, the vertical becomes much more pronounced but for more realistic levels of cant, the vertical component is pretty much negligible. Given the myriad of other factors like the basic accuracy of the rifle, the human element, and the wind, the difference would be pretty hard to discern.
It is IMPOSSIBLE for the higher mount condition to not move the muzzle more laterally than the lower mount for any given amount of cant. Simple geometry (the longer radius) and mechanics (the scope is bolted rigidly to the rifle). Cant the rifle any amount and a higher mounted scope will cause the bore to shift more laterally than will a lower mounted scope. MORE horizontal cant error closer than zero distance, not LESS. The radius from scope bore (LOS, point of aim)to muzzle is longer for the higher mount thus the muzzle will move slightly more laterally caused only by the relative height of the scope mount in this situation. Thus a higher mount will cause slightly MORE cant error at any range closer than zero range than will a lower mount. Beyond zero range the error will also be greater for a higher mounted scope and will gradually increase due to continued divergence of flight path from vertical until the projectile stops. MORE error at longer ranges and progressively MORE error for higher mounts at longer ranges with any amount of cant.
Consider the extreme scenario the target paper is right up against the muzzle of the rifle, and then let's put the two scopes above the bore and cant the rifle 45 degrees. The high scope has a larger radius from the bore, thus it swings out laterally further than the low scope. Thus if I compare where each of the reticles point on the target paper, the high scope is "more wrong". But here's the problem with that...it's only because it is physically impossible to zero the high scope to the point of impact (nor the low scope, for that matter). The erector tubes cannot angle downward far enough. If they could, their errors would be the same. Out at some more reasonable distance, that condition becomes possible and both the high and low scopes have the same error.
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bandg, all I can say is that if I am incorrect, I am in good company, as my statement agrees with that linked in the thread in the OP.... I have copied the text below, you will have to follow the link to see the corresponding diagrams, should you choose to bother....
CHAPTER 4. When a higher scope is better
And now let's see the opposite instance. The rifle still has two theoretical scopes on it, a low and a high one. Both scopes are zeroed at range 'R0' but this time we shoot at distance 'R' which is SHORTER than 'R0'.
The rifle which is zeroed at 'R0' doesn't hit at range 'R' because the bore looks above the target with 'L' (low scope) and with 'H' (high scope) instead of 'D'. The relation of the red, blue and green points can vary with ballistics but 'L' is always MORE than 'H'.
So we aim with the crosshair at a point which is above or below the target with the appropriate amount 'LA' and 'HA'. In this case, when the bore line hits the target plane with 'L' and 'H' above the aiming point and in both cases with 'D' above the target, and when the pellet drops with 'D' then it hits the target.
If we cant the rifle, the bore line is rotated around the LOS but they are different with this aiming method. This means that the radius of the canting error circle is 'L' with the low scope and 'H' with the high scope and 'H' is smaller than 'L'. This means that in this case the higher scope gives LESS canting error.
The key is not the height of the scope, but the distance between the LOS and the boreline at the distance you are shooting, the "canting error circle" described above.... With a high mounted scope that distance is less when you are shooting closer than the range the rifle is sighted at, than it is with a low mounted scope.... I see little point in continuing to argue with you, all you seem to be interested in is saying "That is just wrong"....
Have a nice day....
Bob
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Mount two scopes, one above the other, if they are canted in the opposite direction there is NO WAY the reticles will align!!!
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Ken, that's true for most any meaningful amount of cant. Typically there's around 60-90 MoA of adjustment in the turrets, meaning the erector tube can move +0.5° - 0.75° so that wouldn't be of much use to correct for any significant divergence of the two hypothetical scopes.
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Mount two scopes, one above the other, if they are canted in the opposite direction there is NO WAY the reticles will align!!!
If one scope is mounted directly above the other, with one scope rotated CW and the other rotated CCW, then you are describing scope-cant. That is a different problem and produces a subtly different error than gun-cant. Though many people confuse the two problems.
Scope-cant is a scope mounting issue. It is corrected by mounting the scope so that the vertical retical intersects the bore.
Gun-cant is a gun hold issue and is corrected by holding the scope upright when taking the shot.
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Bob-
You're still just wrong. But as you say, have a nice day.
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If POA matches POI, and your gun/scope are setup correctly, gun cant errors are NOT affected by scope height - period.
Now, if you have a range finding error, or your dope is bad, or your scope is mounted incorrectly, or your gun is not sighted-in correctly - cant errors will be affected by scope height. But that is not strictly a canting error. Only when you have verified that every other issue has been corrected, then you can look at cant errors. There is plenty of bad testing methodology that thinks gun cant is the only problem, when in realty, a combined error existed. From that combined error, they make general statements that are not really true.
The first link that the OP shows:
www.szottesfold.co.uk/2012/03/high-scope-and-canting-end-of-ancient.html (http://www.szottesfold.co.uk/2012/03/high-scope-and-canting-end-of-ancient.html)
I can't really find fault with his methodology or results. It's a good source.
Bandg posted a different link later in this thread:
www.riflescopelevel.com/cant_errors.html (http://www.riflescopelevel.com/cant_errors.html)
That article made some good points, but had numerous errors. Makes the whole suspect.
Just because information is presented in a professional looking manner, does not validate it.
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Jason-
Take the second paragraph in your post #25. It is accurate but I think you are trying to view it the hard way. You don't aim with the bore, you aim with the scope. Take the exact premise that you described there but put the crosshairs on the target dot (your aim point at zero distance) and rotate the rifle (muzzle/bore) below it. That is the way cant works for an actual shot at zero range. Forget holding over or clicking to change zero. That does change everything. Put the crosshairs on aim point at zero distance. Just like you would do to shoot at a target at zero distance. It is basically the same as you described but seems much easier for people to imagine. If you do that you will note, as you mentioned, that the higher mounted scope has more error (it causes the muzzle to move further to the side than does the lower mounted scope) exactly due to the radius. Consider rsternes statement in #13-"a higher scope has LESS horizontal cant error closer than the sighted difference". Nonsense. As you described it has more error, not less.
Scott-
In the description above, the higher scope has more lateral error near the muzzle than the lower scope. I certainly think that should be obvious. It is a small amount but it is present. The DIFFERENCE in horizontal error between low and high mounted scopes DECREASES as the pellet moves toward the zero point. They match at/near the zero point (ie both will hit the aim point). But what has this done? It has established an angle between the two lines of flight shot from the canted position in the horizontal plane. Obviously the angles exist in the vertical plane due to convergence of bore to LOS (the scope) but forget that for a second. Canting the rifle in the way described above establishes an angle in the horizontal plane. The lower scope pellet starts out slightly closer to the vertical line than does the higher scope pellet. But they both CONVERGE (both horizontally and vertically) as they move to the aim point where both impact at the zero distance. BUT WHAT HAPPENS PAST THAT POINT? DOES THAT ANGLE DISAPPEAR? No, it does not. The pellet will drop due to the force of gravity and slow due to resistance but ignoring wind (and other basically negligible factors like spin drift) it will continue along it's original VERTICAL line of flight. But in the case of the higher mounted scope that is a larger angle than the lower mounted scope pellet was moving on. So the pellet from the higher mounted scope continues to now DIVERGE from the lower mounted scope line as it moves beyond the zero distance. Greater cant error from higher mounted scope than lower with that error increasing with distance.
Assume 25 yard zero. The greatest DIFFERENCE between high and low mounts for any degree of cant will be at the muzzle, lessening to the common impact point at zero distance, then increasing to the exact same amount that was present at the muzzle again at 50 yards distance. Simple geometry. Not a lot of error for air gun distances. But beyond that zero point distance the vertical line of flight of the two pellets will PROGRESSIVELY DIVERGE until they stop moving. Both move away from the LOS (the vertical plane) beyond the zero distance but the greater angle for the higher mounted scope means it moves away gradually faster. Greater error for higher mounted scope.
If anyone wants to visually verify this, you would need a correctly mounted scope on your rifle. If you have high mounts you would need to get low mounts and vice versa to compare the angles created but shooting what you have can easily illustrate the angle. For more obvious results I would suggest more cant. The best target to make is a simple sheet with a vertical line and a dot for aim point near the top of the line. Aim dot should be nearer the top of the sheet to keep drop on paper at longer distances. You can use a protractor to put a point at a specific angle from the vertical to make cant consistent-crosshairs always on aim dot and lower vertical hair on the mark you make for consistent cant. Put a target near the muzzle, cant and shoot. Put a target at zero distance, cant and shoot. Put a target at twice your zero distance, cant and shoot. Same cant amount each time is important. In each case you are putting the crosshairs on the target dot. You are not trying to correct your aim to hit the dot but simply aligning the LOS (scope crosshairs) on the dot the same each time. You will see the horizontal angle mentioned above visibly on the targets as the pellets make their holes (with a clockwise tilt it will be groups low/left near muzzle, groups near point of aim at zero distance, and groups low/right further beyond. You will also see vertical movement (bore rise to zero distance and drop beyond) but that is present in all cases and can be ignored for this process. Simply measure the distance from the vertical line through the aiming dot laterally (90 degrees) to the group impact point. Must have little to no wind for this to work. Then to see the difference related to height, mount the scope correctly with the other mounts and repeat the sequence.
Make a little assumption here-25 yard zero and assume you tilt the gun enough clockwise to move the pellet impact point 1" left of vertical near the muzzle (remember, crosshairs always on the aim dot and always the same amount of tilt). That impact point will be low and left of the aim dot near the muzzle. At the zero distance the pellets will hit (impact point) very near the aiming dot. Beyond the zero distance at 50 yards the pellets will impact lower (depending on gun/pellet velocity) but they will again be 1" right of the vertical line (same as at the muzzle). There's that pesky angle again. If you get larger paper for targets and continue to move the target away you will see the pellet falling dramatically lower due to gravity but it will continue to move laterally at a predictable rate due to the angle and distance. Again, any wind will make it very difficult to get consistent results.
I really hate to argue with people about this. But I have done exactly the above. On calm days. In the backyard with air rifles and at my 600 yard range with firearms. I've looked at the targets with the holes in them. I've seen a visible amount of cant move a bullet a couple of feet at 600 yards then immediately (no change in wind) cant the other way and watch them hit a couple of feet in the other direction. If you want to illustrate this to yourself, give it a try. You can go through this process with an air rifle and single mounted scope in an hour or so.
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Take the second paragraph in your post #25. It is accurate but I think you are trying to view it the hard way. You don't aim with the bore, you aim with the scope.
That made me smile because I was thinking about writing something along similar lines when I replied earlier. :) I noticed you prefer to make reference to "swinging the bore", and that's all well and good, and I prefer to make reference to "swinging the scope" because it's physically what I would do if I were sitting at the bench with the rifle resting in front of me. I would leave the rifle where it is and tilt it to one side...that is, "swing the scope". This preference really has nothing to do with an idea of aiming with the bore.
Whether we swing the bore or swing the scope makes no difference but it does seem to make it a bit harder to communicate our concepts to each other.
Take the exact premise that you described there but put the crosshairs on the target dot (your aim point at zero distance) and rotate the rifle (muzzle/bore) below it. That is the way cant works for an actual shot at zero range. Forget holding over or clicking to change zero. That does change everything.
Okay, I'm carefully picturing the the scenario from your perspective....
Put the crosshairs on aim point at zero distance. Just like you would do to shoot at a target at zero distance. It is basically the same as you described but seems much easier for people to imagine. If you do that you will note, as you mentioned, that the higher mounted scope has more error (it causes the muzzle to move further to the side than does the lower mounted scope) exactly due to the radius...
Well, again I acknowledge the difference in the swing radius of the two scopes. No question about that. But the higher scope only has more error if it is not zeroed to the same POA as the lower scope.. For your contention to be true, it assumes the scopes' lines of sight (LOS) and the bore line are parallel. But they aren't. The scopes' erector tubes are angled so as to put the reticles onto a common POA...when both scopes are zeroed, their reticles literally superimpose on top of each other. Whatever error one has by way of canting the rifle, the other has the exact same error.
The obviousness of the larger swing radius makes it very tempting to think the high scope is worse. In fact the author linked in the original post covers this common misconception very early in the article:
CHAPTER 1. Misbeliefs
...An old gunsmith explained it to me in the following way, this is the simplest mistake which says that the higher scope means more offset when canted with the same angle:
(http://field-target.mds-epitesziroda.hu/kepek/CE0_01.gif)
Of course this is right only if we shoot at a paper which is immediately in front of the muzzle. The bore line and LOS are not parallel, and the LOS' of different scope heights intersect on the target so the displacement is the same...
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...Assume 25 yard zero. The greatest DIFFERENCE between high and low mounts for any degree of cant will be at the muzzle...
Do you know the difference between scope-cant and gun-cant? Your statement is true for scope-cant. But if a gun has been setup correctly, scope-cant will not exist.
If you are canting a correctly setup gun, your statement that I quoted above is obviously wrong.
Gun-cant errors are a function of gravity acting on the trajectory at an angle away from vertical. At the muzzle, gravity has not yet affected the trajectory. If the trajectory is not affected, it should be obvious that there will be no gun-cant error.
I now think that you are confusing the calculations used for scope-cant with the calculations for gun-cant. That is a common occurrence when someone attempts to analyze and quantify cant errors.
Think about this:
1) Scope-cant errors can happen even in zero gravity.
2) Gun-cant errors DO NOT happen in zero gravity.
Now - which of those two are you talking about?
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I don't agree, and I'm not assuming parallelism. Parallelism would mean you would never hit the target, you would always hit low. Bore has to converge with scope/LOS. And if you "swing the scope" then you aren't aiming any longer. When shooting, you are looking through the scope and aiming at the target. Cant arises by unintentionally tilting the rifle but a shooter would still be putting the crosshairs on the POA. How else do you aim? The crosshair is the only aim point you have. You can talk about swinging it in theoretical terms and therein arises the confusion. How in the world could you "swing the scope" and still be able to aim"
I am assuming the same zero distance for both high and low scope and the same POA. Assume no cant, scope mounted directly over bore, rifle held level. Everything perfect. Assume a low mounted scope has bore 1" below scope. High mounted scope has bore 2" below scope. Both are SCOPES are aimed at the same POA and at the same distance. You can represent this easily with a horizontal line representing the scope/LOS from front of scope to a target. That line represents both scopes and as you note the reticles are superimposed. But the bore tilts upwards less for the low mounted scope (bore starts closer to scope/LOS) and tilts upward more for the high mounted scope (it starts further from the scope/LOS). This must be true for both to hit at the same point at the same zero distance. Now below that horizontal line (representing both scopes/LOS) draw a first line representing the low mount situation with bore starting 1" below the scope tilting up to the POA and a second line below that representing the high mount situation with bore 2" below the scope (1" below the low mount) again angled upwards toward the POA. Both scopes are level and aimed at the same point (represented by the main horizontal line). The low mount situation starts the bore closer to the scope and it tilts less steeply upwards as it moves to the POA. The high mount situation starts the bore further below the scope but it tilts more steeply upwards to the identical POA. 2 theoretically superimposed scopes with the different mount heights resulting in different bore tilts. Draw it out. That lower line being below the middle line is the difference in low and high mounts. Both bores converge to the single common aim point but the higher mounted scope will have the shot below the lower mounted scope out to zero distance where they meet.
Now introduce the unwanted cant. In actually firing a shot, how could you "swing" the scope anywhere. The scope is your only defined aim point and to hit a target it must be and remain aligned on the target. The cant error results from no longer having the rifle (the bore) directly below the scope. The scope is still aimed at your target (why would you "swing" it off target?) but the bore has moved laterally below the scope.
If this doesn't make sense to you then we are discussing the concept using profoundly different views of mechanics. I'm not capable of viewing it any other way because it isn't logical to me. How do you hit anything without having and keeping the scope aligned on the target? "Swinging" the scope is not something I can practically get my mind around. Obviously anything can be moved in space, tilted, up/down, left/right, whatever direction one wants to move it. But to fire a shot and hit a target the aiming mechanism (the scope in this case) must be aligned directly on the target. Cannot understand "swinging" that.
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Scott-PM sent. I do know the difference. The quote you say is not right for a correctly set up scope/rifle is simple geometry. With a correctly set up scope and rifle and a common zero distance, two different scope heights will produce two different projectile paths that start at two separate points but converge with each other to the zero distance aim point just as each converges with the LOS to that point. They must converge so that each can impact at the zero distance aim point. How can the greatest difference between the two paths be anywhere but at the muzzle if they are converging as they move away from the muzzle?
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Scott-PM sent. I do know the difference. The quote you say is not right for a correctly set up scope/rifle is simple geometry. With a correctly set up scope and rifle and a common zero distance, two different scope heights will produce two different projectile paths...
Not true.
The projectile path from the muzzle to the bullseye is exactly the same regardless of scope height.
The scope has no affect on the pellet's trajectory.
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In actually firing a shot, how could you "swing" the scope anywhere. The scope is your only defined aim point and to hit a target it must be and remain aligned on the target. The cant error results from no longer having the rifle (the bore) directly below the scope. The scope is still aimed at your target (why would you "swing" it off target?) but the bore has moved laterally below the scope.
Okay, I see your aversion to my approach. You want to hold a particular unchanging point of aim, let's call it POA-A, and I can understand why you want to do that. However my interest is exploring the point of aim versus the actual point of impact, and for that it does not matter. In other words when I swing the scope to cant the rifle, I have a new point of aim, POA-B...but then when I fire, I realize my POI wasn't at POA-B. That's all.
That line represents both scopes and as you note the reticles are superimposed.
This. Focus on this part. If both reticles are superimposed on top of each other, and the reticles represent your point of aim, how can one have more error than the other?
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Both are SCOPES are aimed at the same POA and at the same distance. You can represent this easily with a horizontal line representing the scope/LOS from front of scope to a target. That line represents both scopes and as you note the reticles are superimposed. But the bore tilts upwards less for the low mounted scope (bore starts closer to scope/LOS) and tilts upward more for the high mounted scope (it starts further from the scope/LOS).
By the way, I think the bold part is where the logical error arises. The bore does not tilt upward differently for one scope versus the other scope. The bore is fixed, and instead each of the scopes is tilted differently. They have to be in order for their points of aim to be identical.
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Sorry, one more thing :)
After thinking on this some more, it occurred to me perhaps part of the difficulty is a tendency to visualize the reticle more as a physical thing inside the scope tube. Well, it is but the way it operates is something else. Instead try thinking of it as a projection...something of a hologram projected onto the target.
That is the manner in which our two hypothetical scopes have identical points of aim.
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Jason, what you just said is plain silly-"the bore is fixed"? Fixed in relation to what? You say the scope is not fixed (each of the scopes is tilted differently) but the bore is fixed? I described a level line of sight to make it easier to visualize the bore to scope relationship. Neither bore nor scope is "FIXED". Move one and the other moves because they are rigidly bolted together. If the scope is held level, the bore(s) tilt upward. If the bore is held level, the scopes(s) tilt downward. Neither the bore nor the scope is "fixed" in relation to the world. They are fixed only in relation to each other via rigid mounts. And the line of sight and the bore line must converge as they move away from the rifle or you would never have a zero at the crosshair. You would have a pellet flight that starts below the point of aim and falls away from it.
"The bore does not tilt upward differently for one scope versus the other scope". Really? Do you really believe that? It is nonsense. And the way I describe a level scope (the line of sight from eye to target) was only to make that easier to visualize. I never stated anywhere anytime in any manner that the scope was fixed. But the bore is not "fixed" either. The line of sight can be upward, downward, left or right. It depends on where you are standing and where your target is. The bore is not "fixed". The scope is not "fixed". But they are bolted together and move together. It is just easier if you fix one (either scope or bore, doesn't matter) MENTALLY so the change is easier to visualize.
One last time for folks to try to visualize this. Look at one of the horizontal lines running across the page you are viewing. Let that represent line of sight/what the shooter sees through the scope/your aim line. Imagine the shooters eye is at the left end of the line looking through the scope but you are standing 90 degrees to his right looking at the scene from the side. That is the foundation of this example. Looking through the scope, the shooter sees the target with the crosshairs directly centered. Perfectly aimed. But where is the bore? You can do this with just an unmounted scope in which case there would not even be a bore to consider. But the shooter would still see exactly the same thing when looking through the scope-the target and the crosshairs. Now mount a rifle to that scope. While looking through the mounted scope the shooter still sees exactly the same thing-target with crosshairs centered. The rifle is on the left with the shooters eye and the target is at the right end of the line. Take a straight edge and start 1" below the left end of the line (this represents a "low mount" with the scope closer to the bore) and line it up with the right end of the line. That is how a scope must physically pair bore to line of sight in order to make a projectile hit the target. Before Jason says it has something to do with the optics in the scope, realize that you can change the turrets to effect this tilt (internal correction), you can physically shim one end of the scope to effect this tilt (external correction), you can use adjustable mounts to effect this tilt (also external correction) or you can use a tapered mount to effect this tilt (again external correction). It doesn't matter how the correction is done, it only matters how the LOS and the bore are made to approach each other toward the right side. Realize that using any of the correction methods, the view through the scope from eye to target will still be exactly the same. The example only illustrates the RELATIVE scope/LOS to bore tilt that must be present in order for the projectile to hit the target. NOW NOW NOW move the left end of the straight edge down another inch (now it's 2 inches below the horizontal line). This represents a "high mount" with the scope further from the bore). While keeping the right end of the straightedge on the right end of the line, lower the left end to that new point. Now once again the scope/LOS and the bore are pointing at the same spot on the right, the original target. It must be so in order to hit that target. Do the two lines slope the same? Absolutely not. The lower line (high mount) slopes more steeply toward the LOS than does the middle line (low mount). The scope/LOS to bore angle is different for the two height mounts. Neither scope nor bore is "fixed" in the world but they are attached and thus "fixed" only in relation to each other. That's all I have to say on this. It isn't really that complicated but one must grasp the basic concept. I will post no more on this topic thread but will gladly respond to PM's if anyone wants to discuss it individually. Good shooting to all.
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Jason, what you just said is plain silly-"the bore is fixed"? Fixed in relation to what?
It is fixed in relation to the two scopes...the two scope bodies, anyway.
Your contention is that the two scopes give a different error, thus we have to look at what happens when we adjust each scope relative to the bore. That's why the bore is "fixed". After all, if we had those two scopes mounted on a rifle, that's exactly what we would do. We would sit down and zero each of them to the same range.
If we could angle the bore independently of the two scopes, everything is not rigidly affixed...a condition which you raised yourself:
But they are bolted together and move together.
I'll concede the use of "fixed" here is weak but we seemed to be using the term in the same fashion. Again, you were explaining the scenario where you have to angle the barrel differently to make the trajectory coincide with each of the two scopes. We don't angle the barrel, we angle the scopes...more specifically, we angle each of their erector tubes so their reticles--their "projected" representations--align exactly to each other against the target.
And as I've been saying, if the reticles lie on top of each other, there is no way for their errors to differ. I frankly don't understand how you can acknowledge that to be true but continue to argue that they differ.
Lastly, it's rather unbecoming to continue to call people wrong and refer to their arguments as "plain silly" and "nonsense", particularly when you find yourself in a situation where there are at least 4 knowledgeable people calmly attempting to help you understand why this is so.
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Lastly, it's rather unbecoming to continue to call people wrong and refer to their arguments as "plain silly" and "nonsense", particularly when you find yourself in a situation where there are at least 4 knowledgeable people calmly attempting to help you understand why this is so.
^X2, and why I dropped out of this thread.... 'nuff said.... ::)
Bob
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Gun-cant happens when the gravity vector no longer lies in the trajectory plane. Gravity must be part of the equation.
Gun-cant has nothing to do with the shooters viewpoint. Scope does not matter.
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Sorry but when I try to quote these posts it puts my comments in as part of your post. I see what you are saying-assuming the rifle is canted. But how about aim high but don't cant. :D
Space down past the last [/quote] marker. ;D
-Y
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If taller scope mounts are not more cant error producing than lower scope mounts, except at certain ranges, then the inference that scope height does not matter is not true: It matters a lot under certain conditions, and not at all, at others.
My impression is that with low velocity airguns, and loopy trajectories that require a lot of drop compensation, scope cant is easier to detect when the scope is mounted high. Both in terms of awareness to cant while handling the airgun; and in terms of increasing the uncertainty of shot placement where the exact range is not known.
If large POI shifts only occur at cant angles that are easily noticed and avoided, then arguing which scope height is worse seems rather academic. If cant angles really don't matter that much, then we should inform scope companies that include bubble levels with their mounts immediately of the cost saving they could realize by deleting the bubble levels. Ditto for target shooters for whom precision matters a great deal.
I prefer low mounted open sights because their vertical POI uncertainty is much smaller between 10 and 25 yards. With a tall scope mount zeroed at 10 yards, taking a shot at 25 yards while aiming "point blank" results in shooting high by several inches. Sure, you could zero that scope at 25 yards, but then shooting point blank at 10 yards results in a low shot.
The same exaggerated zero errors that occur with tall scope mounts seem to come into play when severely canting a rifle.
Rather than argue about cant errors, my advice would be to mount the scope at a height where you can get a comfortable repeatable cheek weld. Also, to consider the "point blank" target radius you want to hit, and the span of ranges over which you want to achieve that. If you have a reticle with multiple aim points and you know which is best for the ranges your targets of opportunity are likely to appear at, then only the cheek weld consideration matters.
If you are aware of canting your air rifle, concentrate on avoiding it until you no longer have to think about it....
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suscribed
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What you say is true about a low scope mount having a broader point blank range (PBR) at short distances...meaning the shooter does not have to be as concerned with finding the proper holdover/holdunder for shots that are close in. The corresponding advantage to tall mounts is a broader PBR at longer distances. Which of those is more advantageous will of course depend on the particular use of the gun.
If taller scope mounts are not more cant error producing than lower scope mounts, except at certain ranges, then the inference that scope height does not matter is not true: It matters a lot under certain conditions, and not at all, at others.
Tall mounts do not introduce more gun cant error (i.e. tilting the gun) at any range. Or are you referring to scope cant (scope installed incorrectly)?
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Thanks for clarifying the scope height effect on PBR at longer ranges, Jason. This supports the idea of understanding what scope height does, and then factoring in one's intended use (range) in the decision.
I tried to follow the heavy duty arguments (in the legal and scientific sense) that make up the bulk of this thread. I am not going to argue one way or the other; other than to say, for me low mounts seem to have an advantage, because unfortunately I rarely get to shoot airguns past 50 yards - or even that far. So, what happens between 10 and 25 yards is more import to me.
Also, that despite the feeling that tall mounts produce larger cant errors for the shooting I do; that taller mounts make it easier for me to hold a true vertical because there seems to be a stronger vertical reference. In other words, there is no real problem in need of a solution.
So, I am stating my preference, rather than making an argument why anyone who does it differently is "wrong".
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As a HUNTER class FT shooter utilizing "Holdover" mount my scope LOW AS THEY CAN GO. This has my close range dope far less range sensitive so getting the difficult close and small KZ's is easier at the expense of having more drop at further ranges.
This however is mitigated when the scope in use ( 16X ) range finds well. DOPE is dope and if you can break clean shots your still making kills at distance.
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As a HUNTER class FT shooter utilizing "Holdover" mount my scope LOW AS THEY CAN GO. This has my close range dope far less range sensitive so getting the difficult close and small KZ's is easier at the expense of having more drop at further ranges.
This however is mitigated when the scope in use ( 16X ) range finds well. DOPE is dope and if you can break clean shots your still making kills at distance.
Drop is projectile as related to bore-line.
POI is impact point as related to line-of-sight.
Scope height has no affect on drop. So I would say it this way:
"...at the expense of having more drop POI change at further ranges...."
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To mount the scope higher
or lower....? 🤔
I'd say as low as you can and still get your eye positioned in the scope's eye box.
Because:
A higher scope will give me a point blank range farther away.
A lower scope will give me a much closer PBR.
If my quarry is farther away I do have some time to range, check hold over/ turret dials.
But if my quarry is close I have no time for that and need to shoot quickly.
>
That's why I prefer a lower scope. :)
Besides, it makes the gun more compact.
Matthias
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With that clear and precise summary, Matthias; this thread can now be locked.
The only other thing I would add to your "more compact" remark, is that a high scope mount makes a gun feel top heavy - or just plain heavy.
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Do you know the difference between scope-cant and gun-cant? Your statement is true for scope-cant. But if a gun has been setup correctly, scope-cant will not exist.
This guy set up two identical scopes with quick release on a 6.5 Creedmoor. One had the scope reticle aligned to the flat on the receiver. The other had the vertical cross-hair aligned to a plumb line, despite the rifle being slightly canted to match the shooters comfortable hold: youtube.com/watch?v=eCoHG23TQcY
The results may surprise you...
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Do you know the difference between scope-cant and gun-cant? Your statement is true for scope-cant. But if a gun has been setup correctly, scope-cant will not exist.
This guy set up two identical scopes with quick release on a 6.5 Creedmoor. One had the scope reticle aligned to the flat on the receiver. The other had the vertical cross-hair aligned to a plumb line, despite the rifle being slightly canted to match the shooters comfortable hold: youtube.com/watch?v=eCoHG23TQcY
The results may surprise you...
At 1000yrds - not surprising. As long as the reticle was held vertical (no gun-cant), the small amount of scope-cant needed to get the rifle comfortable will be insignificant.
With airguns, we often shoot as close as 10 yards. At 10 yards, scope cant issues will be 100x as much as it is at 1000 yards. It's a function of scope_height/distance_to_target. You would not likely see the error at 1000yards, but you would at 10 yards.
Also - if you are shooting at only one distance (whether it be 10yds or 1000yds), it does not matter at all, as long as you are sighted in (elevation and windage) for that one distance.