Why cant matters to holdover shooters (Super basic)

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Scotton, 😊

thanks for the detailed write up and the innovative way to explain it — with the two long rods. 👍🏼

We have so many people join here every day — there is more than just 1% that needs instruction on these things! 😄



So, keep it coming! 😊

Matthias



PS: A green accuracy ball for you!
Green Ball AGN Accuracy Point. 02.1608587644.png

 
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Super basic is right. Take the intersection of the vertical and horizonal lines of the scope we will call it the point. This scope is set up perfect the vertical line goes right through the center of the bore. Now cant any way you like. Pretty easy to see as you move closer or farther from the point up and down the vertical line with what would be the bore it does indeed change the poi closer and farther with no change in the amount of cant. Trust most can grasp this and tell fact from opinion. 
 
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Do not think it matters if you are a holdover shooter or not. The pellet will have the same path, so the error will be the same when canting, as when using dial, or holdover (asuming using the correct holdover).
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I think it depends entirely on HOW you holdover. Are you using a mil-dot scope and using one of the mil-dots as the aim point? Or are you using a simple crosshair and holding that aim point an estimated amount over the target? The statement by nervoustrigger that started my ongoing disagreement with him was that scope height above bore does not effect cant error. Period. As if it applied to all situations. That was the original statement and that is incorrect because it is overly generalized or too egocentric (how I shoot). Scope height (sight height) does not affect cant error if one clicks to zero (dials) for a known distance. In that case, if the distance is known accurately, then any cant would have little to no effect. When one uses mil-dots as the aiming point for holdover, it becomes a bit of a hybrid situation and I am not certain how much scope height would effect cant error in that situation. The case where sight height does absolutely effect amount of cant error is when one uses the crosshair as the aim point and "holds over" from that perspective. Then, height of the sight does directly effect amount of the cant error produced. Consider a simple cross hair or duplex reticle without mil-dots. How does one "hold over" with that? His focus is on the crosshair and not on a "mil-dot".

Consider an open sight rifle with a "sight height" above bore of 1/2" zeroed at 50 yards. Cant any amount and it doesn't matter-at 50 yards only. Cant this rifle 45 degrees CCW and the bore moves roughly 1/4" off vertical to the right. Still hits almost dead on at 50 yards (slightly more drop but a very minor amount). At 100 yards the shot hits 1/4" to the other side of the vertical, to the left. Now take this out to 500 yards. The 1/4" error is now 2.5". The correct amount of "holdover" can be determined for the known 500 yards and would be consistent for vertical but the cant moves the POI horizontally. There is no "ranging error" to throw into the conversation.

Now take the exact same rifle and correctly mount a scope at 2" high above bore zeroed at the same 50 yards. Cant the rifle the same 45 degrees CCW and the bore moves 1" to the right. Still hits dead on at 50 yards. At 100 yards the POI is 1" LEFT of vertical. Move to 500 yards and the POI is 10" left of aim point. 4 times the "amount of cant error" just related to sight height. All other factors the same. So the general statement that scope height above bore does not effect cant error is wrong. 

One could correctly say that scope height above bore does not effect cant error IF ONE CLICKS TO ZERO. Possibly, one could also say the same about using the mil-dot as the aim point but I am not certain about that as I haven't tried it. When using the central cross hairs as the aim point and "holding over" as I describe above, then height of sight above bore DOES effect cant error. There is no "ranging error" to claim in this as the distances are stated (known) and the same for each rifle. A different amount of "holdover" would be required for each rifle but it could be known and would be consistent for any given range. The varying factor is sight height only. And it does effect cant error when shooting as described above.
 
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I think we are treading over some well-worn ground but when using mildots as the aim point (for a known, accurate distance), you have effectively re-zeroed your scope and that makes the cant error independent of scope height. Both the author of the “ancient myth” article and Scott (scotchmo) have substantiated this point. 

In the previous thread, I finally realized your examples that demonstrate a contrary position fell into the category of ranging error rather than cant error. Soon Scott joined the discussion and apparently arrived at the same conclusion.

Also, in the previous thread we covered the topic of whether it applies in all situations. It applies to both clicking and holdover (compensation made within the scope). It does not apply to compensation done outside the scope (placing the crosshairs on a squirrel’s head so it will drop and hit the heart/lung area). The former approaches are good, and I dare say they represent very nearly 100% of all shooting, at least by people who care enough about their results to be cognizant of factors like cant error. The latter approach is not a good one, though as you say it may be tempting to try it if all you have is a simple crosshair reticle (no mildots or similar subtensions to use as aim points).

Note the thread I linked earlier contains a link to yet another thread which is quite lengthy but goes much deeper into the experimental verification and edge cases. It’s not a light read but covers some very good material for those interested. 
 
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I think we are treading over some well-worn ground but when using mildots as the aim point (for a known, accurate distance), you have effectively re-zeroed your scope and that makes the cant error independent of scope height. Both the author of the “ancient myth” article and Scott (scotchmo) have substantiated this point. 

In the previous thread, I finally realized your examples that demonstrate a contrary position fell into the category of ranging error rather than cant error. Soon Scott joined the discussion and apparently arrived at the same conclusion.

Also, in the previous thread we covered the topic of whether it applies in all situations. It applies to both clicking and holdover (compensation made within the scope). It does not apply to compensation done outside the scope (placing the crosshairs on a squirrel’s head so it will drop and hit the heart/lung area). The former approaches are good, and I dare say they represent very nearly 100% of all shooting, at least by people who care enough about their results to be cognizant of factors like cant error. The latter approach is not a good one, though as you say it may be tempting to try it if all you have is a simple crosshair reticle (no mildots or similar subtensions to use as aim points).

Note the thread I linked earlier contains a link to yet another thread which is quite lengthy but goes much deeper into the experimental verification and edge cases. It’s not a light read but covers some very good material for those interested.
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Once again, read what I posted above. There is no "ranging error" involved. Your statement was overly generalized and thus incorrect. Narrowed down as you have done, it is accurate for that methodology only. As to whether any approach "is not a good one", that is your opinion only. Not all shots are taken off a bench with plenty of time involved.
 
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Yes, I am asserting that shooting without a proper aim point is not a good approach. I mean, technically you are correct that it’s just an opinion but I think it’s reasonable to assume we are in the company of people who care about accuracy so it hardly seems a controversial one.

What do you consider it to be, to shoot without a proper aim point? Good or bad?

And your continued charge that I’ve overly generalized the subject communicates nothing to me other than your unwillingness to read. Not only was my previous post dealing with that very topic, it was also explicitly covered in each of the two earlier threads.

Lastly, I don’t know what you mean about “not all shots are taken off a bench with plenty of time involved.” On its own, it’s a perfectly reasonable observation. I just don’t know what it has to do with the topic at hand. It seems to me if one is in a situation so rushed that there is no time to get the rifle level and find the proper aim point, the decision has already been made to trade away accuracy in favor of speed.
 
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Yes, I am asserting that shooting without a proper aim point is not a good approach. I mean, technically you are correct that it’s just an opinion but I think it’s reasonable to assume we are in the company of people who care about accuracy so it hardly seems a controversial one.

What do you consider it to be, to shooting without a proper aim point? Good or bad?

And your continued charge that I’ve overly generalized the subject communicates nothing to me other than your unwillingness to read. Not only was my previous post dealing with that very topic, it was also explicitly covered in each of the two earlier threads.

Lastly, I don’t know what you mean about “not all shots are taken off a bench with plenty of time involved.” On its own, it’s a perfectly reasonable observation. I just don’t know what it has to do with the topic at hand. It seems to me if one is in a situation so rushed that there is no time to get the rifle level and find the proper aim point, the decision has already been made to trade away accuracy in favor of speed.
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I'll stick with egocentric.
 
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When you turn the turrets that moves the crosshairs and rezeros your scope. Holding over with a mill dot or not changes nothing. Mill dot or not you are still holding over. True at your zero, cant is less of a issue regardless of scope hight. But if you run your zero out far enough the effects will become more apparent. And will show up sooner the greater the distance from bore to scope center because the effect of the cant is greater. The idea that by useing the lower part of your scopes sight picture should lessen the effects of cant because hey your closer to bore. Sounds good but no its not. The scope and bore distance and zero is unchanged all that has is your aim point. It would be nice if we could have discussions like this with out it turning into a fight. I sure as hell dont know everything and have no doubt some of the things i think i know are wrong. If you can further my understanding please do.
 
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Do not think it matters if you are a holdover shooter or not. The pellet will have the same path, so the error will be the same when canting, as when using dial, or holdover (asuming using the correct holdover).
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I think it depends entirely on HOW you holdover. ...

Consider an open sight rifle with a "sight height" above bore of 1/2" zeroed at 50 yards. Cant any amount and it doesn't matter-at 50 yards only. Cant this rifle 45 degrees CCW and the bore moves roughly 1/4" off vertical to the right. Still hits almost dead on at 50 yards (slightly more drop but a very minor amount). At 100 yards the shot hits 1/4" to the other side of the vertical, to the left. ...
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tor47 is correct.

bandg, you are describing aiming errors which can be affected by scope height, but they are not gun cant errors.

Gun cant errors are caused by gravity and have nothing to do with the scope. So holdover and clicking are equally affected.

Aiming errors, including ranging errors, are affected by scope height, whether the gun is canted or not.


"...Consider an open sight rifle with a "sight height" above bore of 1/2" zeroed at 50 yards. Cant any amount and it doesn't matter-at 50 yards only. Cant this rifle 45 degrees CCW and the bore moves roughly 1/4" off vertical to the right. Still hits almost dead on at 50 yards..."

That would be true for a laser because it's not affected by gravity, but at 50yds, a pellet is greatly affected by gravity. So any measurable cant does matter. You would not be "almost dead on". You would be about 5" off horizontally and 2" low from the aim point. That's what you get when you cant a 7" drop trajectory at 45 degrees.

horizontal error = drop x sin(cant_angle)

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

"...At 100 yards the shot hits 1/4" to the other side of the vertical, to the left...."

Since you were sighted to hit dead on at 50yds, but were shooting at 100yds, that would produce an aiming error (ranging error). A real trajectory (not a laser) curves downward. In the real world, with 45 degree cant at 100yds, your pellet will impact a couple of feet from your aim point. That 1/4", 50yd aiming error related to scope height becomes trivial.

Try this exercise: Sight your airgun for 50yds. Cant your gun 45 degree on the bench and try and hit the target. - good luck.
 
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Changing the scope height merely changes which mildot is the proper aim point for a given distance.

The implications of that are as follows.

Let’s say I have a rifle with two scopes on it, one above the other. Both are zeroed for 50 yards. I want to shoot at 100 yards. I need to use a different mildot for my holdover with these two scopes (the erector tube in the upper scope is angled more sharply downward). If I cant the rifle 5 degrees and use the proper mildot with each scope, the resulting error on the target at 100 yards will be identical.

If instead I used the same mildot as the aim point for each scope, the error at the target will be different. That is a ranging error. 

I don’t know if that is the scenario you are describing. It’s just one that seems to be a common source of confusion and I’m fishing for a more specific detail on which we disagree.

Or perhaps point out where Andras’ experiment goes wrong.
http://www.szottesfold.co.uk/2012/03/high-scope-and-canting-end-of-ancient.html?m=1
 
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Changing the scope height merely changes which mildot is the proper aim point for a given distance.

The implications of that are as follows.

Let’s say I have a rifle with two scopes on it, one above the other. Both are zeroed for 50 yards. I want to shoot at 100 yards. I need to use a different mildot for my holdover with these two scopes (the erector tube in the upper scope is angled more sharply downward). If I cant the rifle 5 degrees and use the proper mildot with each scope, the resulting error on the target at 100 yards will be identical.

If instead I used the same mildot as the aim point for each scope, the error at the target will be different. That is a ranging error. 

I don’t know if that is the scenario you are describing. It’s just one that seems to be a common source of confusion and I’m fishing for a more specific detail on which we disagree.

Or perhaps point out where Andras’ experiment goes wrong.
http://www.szottesfold.co.uk/2012/03/high-scope-and-canting-end-of-ancient.html?m=1
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It's not a "ranging error". You stated the yardage. You can call it an aiming error but it cannot be a "ranging error" by definition. And again, consider the other non-mil dot method of holding over that I described above and try to tell me that your statement that sight height has no effect on cant error is accurate in that situation. You cannot because it isn't. You can state that it "isn't the way to shoot" but that doesn't address the mechanics of the situation. Your statement that sight height doesn't effect cant error is just wrong because even though it may not effect cant errors for the way you shoot doesn't mean that is the only way to shoot and sight height DOES affect cant error when one shoots as I described above. It may not be the ideal way to aim and is, as you stated, probably not used a lot anymore. But it is used. And as to gravity, I see the drop/cant error connection as correlation, not causation. Cant error isn't "dependent" on drop or gravity. Cant error is correlated with drop because both change in a predictable manner. Cant error, however, is a constant along a line of horizontal displacement and drop is a progressive change with distance. One does not cause the other.

As to scotchmo's assertion that you will hit a couple of feet off target at 100 yards if canted 45 degrees, I would say that is entirely dependent on the trajectory of the projectile. It will be much more correct with a low velocity air gun and much less correct with a higher velocity projectile. A very fast flat round would drop less between 50 and 100 yards than would a slow heavy diabolo pellet. Gravity will cause each projectile to have a different ballistic arc in the vertical plane but the horizontal movement related to cant angle would remain constant.

We will not agree. That certainly seems clear. Hope all reading this thread can have a healthy and Merry Christmas. 




 
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Bandg, my last reply was to fuznut. I was not asserting you were making a ranging/aiming error in this thread, though you did as explained by Scott.


And once again, I never stated there is a prescribed way to shoot. The circumstances under which scope height matters and when it doesn’t has been discussed in detail both here and in the linked threads. If you click or use mildots, it doesn’t matter. Otherwise it might.
 
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...
...Cant error isn't "dependent" on drop or gravity. Cant error is correlated with drop because both change in a predictable manner. Cant error, however, is a constant along a line of horizontal displacement and drop is a progressive change with distance. One does not cause the other.

As to scotchmo's assertion that you will hit a couple of feet off target at 100 yards if canted 45 degrees, I would say that is entirely dependent on the trajectory of the projectile. It will be much more correct with a low velocity air gun and much less correct with a higher velocity projectile. A very fast flat round would drop less between 50 and 100 yards than would a slow heavy diabolo pellet. Gravity will cause each projectile to have a different ballistic arc in the vertical plane but the horizontal movement related to cant angle would remain constant.
...
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"...Cant error isn't "dependent" on drop or gravity...."

GUN cant errors are 100% dependent on gravity. They would not happen in a weightless environment.

SCOPE cant errors are not dependent on gravity. Scope cant can result in an aiming error. It can happen even in a weightless environment.

"...As to scotchmo's assertion that you will hit a couple of feet off target at 100 yards if canted 45 degrees, I would say that is entirely dependent on the trajectory of the projectile...."

The trajectory is a result of gravity, so gun cant error is dependent on gravity. Gun cant error for a laser would be "none" as it is a straight line. Gun cant error for a 30-06 at 2800fps would be a couple of inches. Gun cant error for an 850fps pellet would be a couple of feet. And none of those depend on the scope height. Since we are talking airguns here and not laser guns or supersonic projectiles, "couple of feet" is a good estimate for this discussion..

"...Gravity will cause each projectile to have a different ballistic arc in the vertical plane but the horizontal movement related to cant angle would remain constant..."

With gun cant the horizontal error is directly proportional to drop (average velocity). What you said is true for scope cant, but not for gun cant.

For gun cant: horizontal error = drop x sin(cant_angle)

https://www.gatewaytoairguns.org/GTA/index.php?topic=72099.0

Notice it says "cant errors". It can help you separate "gun cant" from "scope cant". People often say "scope cant" when they really mean "gun cant", or vice versa. They are two different, though somewhat related problems. If unsure, best to just say "cant errors".






 
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"Aside from the math" which is hard for me to think about all of the relationships involved LOS/LOB/scope height/canted reticle in the scope, etc, then looking into the practical aspects of impacting (medium??) sized targets, as well as to not let new shooters get freaked out over this subject, please forgive my layman's take on the subject.

What will normally happen is that smallish Cant error will be "swallowed up in the noise" of - wobble, windage error, drop error, spin drift, aerodynamic jump, scopes not tracking, and whatever else I'm not thinking of right now. How do I know??? Because if someone like me that has a highschool education, and isn't particularly bright, can win long range championships without using a bubble level "some of the time" in centerfire Field Course steel events, and FT state wins, and NRL22 wins, then surely having some Cant in the system isn't a terrible thing. 

In the human system we naturally try to set the vertical crosshair plumb to the target which is partly why we don't see as much error from Cant as expected. Also, for the last 3-4 years I've been setting the crosshairs in my scopes to "look" straight which appeals to me greatly, rather than getting everything perfectly plumb and level which always makes the reticle look exaggeratedly and annoyingly counterclockwise to me. I took all my Horus ASLI off my scopes as well.

I suppose if I was on a $20,000 hunt with a once in a lifetime tag then I might go the extra mile and put on the ASLI but otherwise I'm not going to be bothered with it.

Happy shooting and Merry Christmas.




























































































































 
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Congratulations on your successful shooting. If I recall what I've read, David Tubbs also was pretty good at shooting and I believe he did something similar-setting his reticle to a comfortable spot for shouldering the rifle and not to a "level" position in relation to the rifle. And there is a youtube video showing a guy doing exactly this thing with no problem hitting targets at long range. I've noticed personally that I can spend a lot of time getting a reticle "level" and then pick up the rifle later and it looks off. Once I force myself to shoulder the rifle more precisely it then looks "normal" again. I would think that having it "aligned correctly" would allow for absolute maximum precision but as you note it isn't the be all and end all for successful shooting. Merry Christmas to you and all here.
 
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Scotchmo

Please excuse my ignorance. But assuming both gun and scope are set up correctly how is it possible to have cant in one independent of the other?
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The two circled in red have the scope mounted correctly but the gun is canted when the the shot is taken. The resulting error would happen even with open sights, so it is independent of the scope.

cant-01.1608845828.jpg



 
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