CANT , and it's effect ?

[Micro]

The prob with canting comes from our aiming . What part of that do we not agree on.??? Sorry but i cant tell lol.

The part about higher mounted scopes causing or magnifying aiming errors described as canting. We agree that in this case canting is an aiming error.

... I read through the AGN post you linked and even "Scott" stated in that post that there may be "some cases" where higher mounts cause more cant errors. There can't be "some cases". It either happens or it doesn't. ...

That is true, and there are also "some cases" where higher scope mounts cause less "cant" errors.

When your POA does not match your intended POI, then errors resulting from cant will be affected by scope height. But is that really a cant error? I consider it an aiming error, the same as miss-ranging. True holdover (aiming above the intended POI) errors and ranging errors are both aiming errors, and both are affected by scope height. High scopes make both of them worse at closer range, and less at longer range.



If you are clicking-on or using vertical graduations on the reticle as holdover aim points, then scope height has no affect on gun cant errors. Gun cant errors are determined by cant angle and amount of projectile drop - and that's all.

I like this response, because it considers canting as an aiming error or undesirable which can be exasperated through higher scope mounting. In my last example I demonstrated a condition in which the axis of the bore maintains the same relationship to the target throughout a full rotation regardless of site height - in that example, the scope could be mounted at any distance from the axis with absolutely no effect from canting or rotation, but that does not take into account what happens when we aim. Should Carmichael have changed his statement to, "The scope should be mounted as high as comfortably possible" ? My aiming error isn't something that happens occasionally, it happens every time I aim - even if that error is infinitesimally small; it is more likely to happen with a scope which is mounted higher than one that is mounted lower which is relative to my ability to compensate for it. My guns don't aim or fire themselves, they are manipulated and controlled by myself and my ability to do that without error is inhibited by a higher mounting position and enhanced by the lowest, comfortable position. Now bash away!

 

[Micro]

It so happens the apology / concession you are looking for is contained in the AGN thread I linked earlier.

No, he apologized too soon, and I quote, "...I have to say, @scotchmo, you were right! A slight but, this only holds for a certain range where the scopes will be zeroed on..."



Then the response - as simply stated earlier, it either can or cannot: 



"I re-canted 

 some things I said in my last post. It is possible to come up with some specific instances where scope height could affect cant. Unusual circumstances. Not normally encountered but possible. In most cases of cant error, scope height does not matter...."

 

[nervoustrig]

It is possible to come up with some specific instances where scope height could affect cant. Unusual circumstances. Not normally encountered but possible. In most cases of cant error, scope height does not matter...."

Thumbs up! Bandg and I have butted heads on this subject in the past and I've acknowledged numerous times that it matters only in the edge case where one is shooting without a proper aim point. After a while it gets annoying to belabor the point...if we care enough about precision shooting to care about cant error, we will not be taking shots without a proper aim point. The nice thing about a mildot scope is that we are zeroed for any distance, meaning we always have a proper aim point. And that's the fundamental reason why the open sights experiment is an apples and oranges comparison.

 

[Micro]

It is possible to come up with some specific instances where scope height could affect cant. Unusual circumstances. Not normally encountered but possible. In most cases of cant error, scope height does not matter...."

Thumbs up! Bandg and I have butted heads on this subject in the past and I've acknowledged numerous times that it matters only in the edge case where one is shooting without a proper aim point. After a while it gets annoying to belabor the point...if we care enough about precision shooting to care about cant error, we will not be taking shots without a proper aim point. The nice thing about a mildot scope is that we are zeroed for any distance, meaning we always have a proper aim point. And that's the fundamental reason why the open sights experiment is an apples and oranges comparison.

Thanks for the history - good to have some back round to gain perspective which I am lacking or ignorant. I understand the annoying aspects of rehashing old discussions or relationships that evolve on forums and I hope that this statement is viewed as offered with an element of respect. Although, the comment about the reticle, etc. was meant to form a comparison, it really goes without saying, the addition of aiming/ranging points are a huge advantage - not a gimmick or better left out because of the confusion they may cause. Thanks again for responding!

 

[Scotchmo]

If "clicking-on", then I agree with you 100%. I've never disagreed with that. The rest is not correct, IMO. With "aiming over", you eliminate "ranging error" by knowing exactly how much you need to "aim over". Is that a guess with a first shot? Probably. But focusing a scope to get a distance is also a guess. A much more precise one, but still a guess. 

...

As to using the mil-dots for holdover, I am not as certain of the effect with that method but I will still say that I BELIEVE that it is the same as I've stated. This is WHY I believe it would be the same-

Take 2 identical rifles, same pellet, same velocity, same zero distance (assume 30 yards), but shooting with separate low and high scopes. Assume for example that the low setup needs 3 mils holdover to hit center at 90 yards and the high only needs 2 mils holdover to hit center at the same distance. Shoot the low setup uncanted with 3 mils holdover and hit center. No "ranging or aiming error". Cant 5 degrees CCW (as viewed from behind) and you shoot low and left. Still no "ranging or aiming error" as you were using the correct mil-dot to hit center but you canted, causing the miss. Now repeat with the higher mounted sight. Shoot uncanted with 2 mils holdover and hit center. Again, no "ranging or aiming error". Cant 5 degrees CCW as before and you hit further left and, I BELIEVE, slightly less low. ...

Clicking or holding over using mil-dots is effectively the same , i.e. - scope height has no affect on gun cant errors. However, moving the cross up above the the target along a canted reticle will cause an aiming error, and in your example of the low scope with 3 dots x 5 degree, the error will actually be greater than the high scope with 2 dots x 5 degrees.

"...Now repeat with the higher mounted sight. Shoot uncanted with 2 mils holdover and hit center. Again, no "ranging or aiming error". Cant 5 degrees CCW as before and you hit further 1/3 less left and, I BELIEVE, slightly less low. ..."

So in that case the high scope has less so called cant error than the low scope.

In the diagram below, I'm showing only the aiming error and not the canted trajectory:

For clicking and reticle/dot holdover there is no aiming error from canting the gun (two views on left). When holding above the target, canting the gun does cause an aiming error (two views on right).

Gun cant errors are caused by gravity acting on the trajectory of the projectile and they are not affected by scope height. How can looking at the target from a higher or lower angle change the impact point? It won't. Scope cant errors (including aiming above the target with a canted gun) are aiming errors and are affected by scope height, and they are worse for a low scope at far targets.

 

[lbc_PSI]

In the diagram below, I'm showing only the aiming error and not the canted trajectory:

I’m sorry. I’m not tracking on the above statement. Trajectories don’t “cant”. Did you mean something else?

 

[Scotchmo]

In the diagram below, I'm showing only the aiming error and not the canted trajectory:

I’m sorry. I’m not tracking on the above statement. Trajectories don’t “cant”. Did you mean something else?

I meant what I said. The following example of what I did not show might clear it up for you. - The ideal (intended) trajectory will lie in a single vertical plane (green - "Vertical trajectory") as seen on edge. That is not the case when gun cant is present (red - "Cant Trajectory"):

Since Bandg was discussing the canted LOS error/scope cant, and not the trajectory error, I did not show the canted trajectory in the earlier post. In reality, you would need to consider the cant of the reticle AND the trajectory.

 

[bandg]

scotchmo

"Scope cant errors (including aiming above the target with a canted gun) are aiming errors and are affected by scope height, and they are worse for a low scope at far targets."

Faulty logic. The ONLY reason to "aim" above the target (using the crosshair) would be because you are shooting at a different range than that zeroed for. And most people would not cant the gun intentionally. It is an error done unintentionally. Since "aiming above" would only be done intentially for hitting a target at distances other than the zero distance, and if such "aiming over" is done in a correct amount, it would result in a consistent hit on target if the gun is held vertically. I do not see how anyone could consider this an "aiming error" as the process of aiming is to align the eye throught the sight to a point that would allow the projectile to hit the target. When you shoot at the same target but introduce cant, you still have the crosshair held in the correct "aiming over" point used prior to hit the target, but you miss. Not because of an "aiming error", but because of the cant. The sight is what we aim, not the bore directly. The bore always follows the sight but not in the same line. Consider a 2" and a 4" high scope each zeroed for 20 yards. Both could be "aimed over" a correct amount for each to consistently hit a target at 80 yards. Obviously a slightly different amount of "aim over" for each but each one using it's own correct "aim over" would hit the target consistently. Such isn't an "aiming error" because you are "aiming" where you need to hit the target at that distance.

But then, cant is introduced in error. The shooter is still holding the crosshair on the correct aiming spot to hit the target IF NOT CANTED. The shooter is "aiming at" the point where he just shot to hit the target when holding level, but with the INADVERTENT cant, he misses. How in the world can anyone call this an AIMING ERROR???? It is an unintentional error for sure, but you are aiming the SIGHT EXACTLY where you just did to hit the target when level. We don't "aim" through the bore. We "aim" our sight and the bore follows. Crosshair on the aim point and gun vertical you hit, crosshair on the same aim point and gun canted you start to miss. Simple. This is absolutely an error, but in no way is it an "aiming" error.

And to your incorrect point about far targets, since a specific convergence angle is set between bore and scope AT ZERO, and that angle is steeper for the higher mounted scope (remember, common zero for both at 20 yards in this example), when cant is introduced the angle is still steeper due to the established radius scope to bore. Think about a 2" high scope vs. a 4" high scope, both hitting at that 20 yard zero. Lay them on their side (90 degrees of cant, either side). When fired, both will "drop" the same amount because only gravity is causing the vertical drop and both are now horizontal. But at the 20 yards distance the low scope shot has moved 2" laterally while the high scope shot has moved 4" laterally. Continue to 80 yards. Since the ANGLE OF CONVERGENCE OF BORE TO SCOPE IS FIXED AT ZERO, the 2" high scope shot will have moved 6" laterally at 80 yards. It moved back to the vertical by 20 yards and then 2" laterally for each additional 20 yards due to the FIXED CONVERGENCE SCOPE TO BORE ANGLE. But the 4" high scope will have moved 12" laterally at 80 yards. Again back to the vertical by 20 yards but now a 4" movement, and then 4" laterally for each additional 20 yards. Geometry. A higher mounted scope will always produce more LATERAL movement than will a lower mounted scope, and progressively more with distance from zero, when shooting this way.

 

[nervoustrig]

By “aiming above the target”, I’m understanding him to mean a simplified holdover...one not done with mildot markings, but one done by placing the crosshairs above the target. If the gun were held true to gravity, the pellet will fall and hit the target as intended. But if the gun is canted, the pellet will not drop to a spot a little further down on the reticle. It will drop to a point a little further down and also to the side somewhat. That error is affected by sight height because it was made without a proper point of aim. Thus it is an aiming error.

 

[Scotchmo]

scotchmo

"Scope cant errors (including aiming above the target with a canted gun) are aiming errors and are affected by scope height, and they are worse for a low scope at far targets."

Faulty logic. The ONLY reason to "aim" above the target (using the crosshair) would be because you are shooting at a different range than that zeroed for. And most people would not cant the gun intentionally. It is an error done unintentionally. Since "aiming above" would only be done intentially for hitting a target at distances other than the zero distance, and if such "aiming over" is done in a correct amount, it would result in a consistent hit on target if the gun is held vertically. ....

True. It only becomes an aiming error when you cant the gun. Intentional or unintentional, the result is the same.

I was showing your rarer instance of aiming (true holdover) where scope height does affect the amount of error when canted. Outside of that, scope height has no affect on gun cant error when using reticle holdover or clicking.

If you are shooting at the distance that the gun is zeroed for, the amount of poi error is then determined by the projectile drop and degrees of cant. That is not affected by scope height.

 

[bandg]

 

nervoustrig

By “aiming above the target”, I’m understanding him to mean a simplified holdover…one not done with mildot markings, but one done by placing the crosshairs above the target. If the gun were held true to gravity, the pellet will fall and hit the target as intended. But if the gun is canted, the pellet will not drop to a spot a little further down on the reticle. It will drop to a point a little further down and also to the side somewhat. That error is affected by sight height because it was made without a proper point of aim. Thus it is an aiming error.



You are correct in what I am referring to, what you are calling a simplified holdover. I have not tested the process with mil-dot holdovers to state precisely whether it works the way I described for this method but I think it may. Could be wrong. If clicking to NEAR zero then no, scope height has absolutely no effect on cant error. As to longer ranges where a second zero is utilized, I believe scope height WILL effect cant error. When using what you refer to as a simplified holdover, scope height will absolutely positively effect cant error. But what you refer to is what I was describing. It certainly isn't the most accurate way to shoot but in some cases it may be the only way. When I was young, it is the way EVERYONE shot. Few people had mil-dot scopes. A duplex reticle was a luxury. I learned to shoot that way and I understand how it works. It usually isn't the best way to shoot if other options are present. It is still often very good for a shot that needs to be taken quickly. The rest of your view (and that of scotchmo and others) is semantics. The only thing a shooter has to "aim" with is the sight. If you are "aiming" at a spot over the target while held correctly vertically and hitting your target, that isn't an "aiming error". It is what a shooter can do. But "aiming" at the same spot with cant error is still "aiming" at the same spot. The "aim" isn't the error, the cant is the error. No one intends to cant. They "aim" to the best of their ability. Aligning the sight off the spot WOULD be an "aiming error". What I am describing is not, in my view. In what I describe, the shooter is aiming exactly what he has available to aim (the sight on the gun) exactly where it APPARENTLY needs to be aimed to hit the target (the spot noted) within his ability of perception. Is is a bad shot? Yes. Is it an error? Yes. A cant error. Simply rotating the gun back to level would correct the error and produce a hit, with the same point of aim by the shooter. How can such be an "aiming" error?

My disagreement with you, scotchmo, and others who agree with you is partially based on the different ways of taking a shot. It is also based on the generality of the original statement made long ago. "Scope height does not effect cant error". Period. Finito. Not "scope height rarely effects cant error" or even "scope height almost never effects cant error", but simply "scope height does not effect cant error". For many (probably most) shooters and methods used, the first two are probably entirely accurate. The latter has never been accurate, is not accurate now, and never will be accurate. Because it is overgeneralized.

 

[Scotchmo]

nervoustrig
...I have not tested the process with mil-dot holdovers to state precisely whether it works the way I described for this method but I think it may. Could be wrong. ....

My disagreement with you, scotchmo, and others who agree with you is partially based on the different ways of taking a shot. It is also based on the generality of the original statement made long ago. "Scope height does not effect cant error". Period. Finito. Not "scope height rarely effects cant error" or even "scope height almost never effects cant error", but simply "scope height does not effect cant error". For many (probably most) shooters and methods used, the first two are probably entirely accurate. The latter has never been accurate, is not accurate now, and never will be accurate. Because it is overgeneralized.

"...Could be wrong...."

You could be wrong and are wrong about that first point as each stadia on the vertical reticle represents a different zero. As long as you use the correct one, it does not matter.

"..."Scope height does not effect cant error". Period. Finito. Not "scope height rarely effects cant error" or even "scope height almost never effects cant error", but simply "scope height does not effect cant error". ..."

When did I say that? Here is what I would say:

Scope height does not effect GUN cant error. Period. Finito

Scope cant is a different issue. You are mixing up the two.

 

[Micro]

Honestly, which is the myth, and which is not? Does scope height matter with respect to cant; it doesn't at the zero in theory - except for slight influences, though the trajectories are different. the effect is worse at greater range for a lower mounted scope, but the reverse for lower mounting within the range up to the zero point, because the trajectories are different or angle to the zero. Which difference is greater between the two - closer or further. 

 

[bandg]

Nope, I'm not. Once you tighten scope mounts down, you cannot "cant" one without "canting" the other. Once mounts are tightened, they move in unison. One cannot move without the other after that point. And I'm ignoring the situation of the scope not being correctly aligned with the gun. I'm referring to everything being "level" as to gun/scope relationship-gun level, scope level, reticle "intersecting" bore. All of my views have been predicated on that, not on any misalignment you want to try to attribute it to.

Unless I'm mistaken, you've said that "drop causes cant error" or something very similar. If that indeed is what you said and I do believe it is, then you are simply incorrect. Consider the same situation as above with a 4" high scope-zeroed at 20 yards. You want to break an aspirin at 20 yards. You could hold over and hit that aspirin if you knew exactly how far away it was, knowing exactly how much holdover you needed to hit it, and if you DID NOT CANT. But if you cant the gun just enough to miss the aspirin laterally (gun rotates, scope rotates=CANT) then you will MISS the aspirin to the side while the pellet is still rising toward LOS. The cant that causes the movement of the bore to the side creating the miss will absolutely also REDUCE the amount of rise toward LOS but not completely eliminate it.

We simply will never agree on this. Didn't then, still don't, and won't in the future. You completely lost any agreement from me by stating that a lower scope would cause more cant error than will a higher scope at longer ranges.

 

[Michigander]

Way too technical a discussion for me. But with regard to rifle cant, I think it helps to have a mental picture of what is going on.

Consider a rifle with an aiming axis and a bore axis separated by some distance. If parallel, a pellet will strike below the aiming axis by an amount equal to the separation between the axes, plus the drop at the target distance. You can bring the pellet strike onto the aiming axis by tilting the bore axis up by an amount needed to compensate for the separation plus drop. The greater the separation, the larger the angle between the bore and aiming axis.

Now consider an extreme cant of 90 degrees CCW. The rifle has been rotated around the aiming axis. The bore and aiming axis are now in the same horizontal plane, with no elevation compensation and the pellet will hit low by the amount of drop at the target distance. But the bore is now pointed to the left of the aiming axis, and the pellet will hit left by an amount determined by the angle between aiming and bore axes. Since the magnitude of the angle is related to the amount of separation between the axes, the rifle having the greater separation of axes will hit further left.

Effects at intermediate amounts of rifle cant are of course intermediate.

Edit: My statement about the angles between sight line and bore line being different dependent on sight height was correct. But my conclusion that this difference would be reflected in cant behavior was wrong as explained in subsequent postings.

 

[bandg]

Way too technical a discussion for me. But with regard to rifle cant, I think it helps to have a mental picture of what is going on.

Consider a rifle with an aiming axis and a bore axis separated by some distance. If parallel, a pellet will strike below the aiming axis by an amount equal to the separation between the axes, plus the drop at the target distance. You can bring the pellet strike onto the aiming axis by tilting the bore axis up by an amount needed to compensate for the separation plus drop. The greater the separation, the larger the angle between the bore and aiming axis.

Now consider an extreme cant of 90 degrees CCW. The rifle has been rotated around the aiming axis. The bore and aiming axis are now in the same horizontal plane, with no elevation compensation and the pellet will hit low by the amount of drop at the target distance. But the bore is now pointed to the left of the aiming axis, and the pellet will hit left by an amount determined by the angle between aiming and bore axes. Since the magnitude of the angle is related to the amount of separation between the axes, the rifle having the greater separation of axes will hit further left.

Effects at intermediate amounts of rifle cant are of course intermediate.

BINGO, we have a winner. I just sent an email to another poster with this exact illustration.

 

[Micro]

Does that mean it's not a myth?

 

[nervoustrig]

In the above example, the point of aim is no longer the intended point of impact. That seems to be a recurring cause of disagreement...the distinction between an aiming error and a cant error.


If we could mark the point of aim on the reticle—imagine putting a little dab of White Out on the reticle—representing how far the pellet will drop at, say, 80 yards. Do that for each of our two scopes, one low scope and one high scope. These painted dots will be at slightly different distances from the crosshair, owing to the scopes being at different heights. Our two scopes are mounted on the gun simultaneously. Then we turn the gun 90deg CCW and aim using one of our white dots—which superimposes onto the white dot of the other scope. Then we squeeze the trigger. The point of impact will be somewhere other than where we aimed because we had the gun canted. And that errant point of impact will be wrong by the same amount from each of our overlapped white dots. The error is no worse for the high scope than the low scope. 

 

[Scotchmo]

...
Now consider an extreme cant of 90 degrees CCW. The rifle has been rotated around the aiming axis. The bore and aiming axis are now in the same horizontal plane, with no elevation compensation and the pellet will hit low by the amount of drop at the target distance....

You got that part right. The vertical equation as it relates to drop and gun cant angle:

vertical error = drop x (1-cos(cant_angle))

...But the bore is now pointed to the left of the aiming axis, and the pellet will hit left by an amount determined by the angle between aiming and bore axes. Since the magnitude of the angle is related to the amount of separation between the axes, the rifle having the greater separation of axes will hit further left.

You got that part wrong. The once vertical compensation for the drop distance is now horizontal, so it will hit left an amount that is equal to the drop. The gun does not care where the viewing angle/position is, so the sight height or angle is not part of the equation. The horizontal equation as it relates to drop and gun cant angle:

horizontal error = drop x sin(cant_angle)

For your the 90 degree example above, sin(90) = 1, and cos(90) = 0.

Your 90 degrees is a fairly extreme example but it does show the point well. The equations works equally well for any angle from vertical.

http://www.scoplevel.com/

 

[Gunnertrones]

The trajectory will be the same whether the scope is mounted high or low. All agree. So again, let us oversimplify: