Buble level anti cant device

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If you're shooting at the distance your rifle is zeroed, then NO it does not matter what your scope height is.

But (BUT!) @broekzwans is correct to say that cant only worsens with additional scope to bore height. If we were all viewing our target from the same height as the bore (like the beginning of a James Bond movie) there would be no such thing as cant! 

Cant starts to really matter when you're shooting below or beyond your zero and relying on some portion of the vertical reticle (a mil dot for example) to hold on the target.

 
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It even matters at the zeroed distance. When you cant, let's say 5 degrees (i know an awful lot) the horizontal distance between your scope and bore becomes greater and the vertical distance/height of the scope from the bore becomes lower. Thus if you cant you lower the scope height whichs changes it's first crossing point of the optics with the trajectory. When using trigoniometrics you can calculate that the distance that the pellet will horizontally differ from it's intented POI will increase with scope height. extending the distance will make it even worse

One thing you can also say is that with higher mounts the drop due to cant will lower. The same idea as the difference in scope height between HFT and FT. HFT shooters want to have a flatter trajectory in the apex of the trajectory and thus use lower mounts, FT shooters want a flatter trajectory after the apex of the trajectory so they use higher mounts. FT shooters have to use less clicks to dial the distance after the apex due to this. Check chairgun for this ;)

I can give mathematical prove of this but I'll do that tomorrow, it's already half past one at night where I live :p I need to catch some sleep :)
 
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"Scotchmo"Brian.in.MI and broekzwans,
You are confusing line-of-sight with trajectory. Scope height changes your point of view (LOS). CANT changes the direction that gravity pulls relative to the gun-scope system. Gravity affects the pellet path, but not the LOS. High scope or low scope, LOS is unaffected.

broekzwans,
I await your mathematical proof.
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@scotchmo We are not confusing anything. 

What we are talking about is the effect of cant when shooting beyond (or below) your zero. If that's the case, the effect of scope height is indisputable when using some portion of your reticle to hold on the target.

Do you dispute that scope height matters (as it relates to cant) when shooting outside of your zero? Or that higher scope mounting exacerbates the effect of cant? 

I await your explanation 

 
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"Brian.in.MI"
"Scotchmo"Brian.in.MI and broekzwans,
You are confusing line-of-sight with trajectory. Scope height changes your point of view (LOS). CANT changes the direction that gravity pulls relative to the gun-scope system. Gravity affects the pellet path, but not the LOS. High scope or low scope, LOS is unaffected.

broekzwans,
I await your mathematical proof.
Click to expand...
I think what we are talking about here is the effect of cant when shooting beyond (or below) your zero. If that's the case, the effect of scope height is indisputable when using some portion of your reticle to hold on the target. Am I missing something?
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Effect of cant is the discussion point here yes .
 
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"Brian.in.MI"
"Scotchmo"Brian.in.MI and broekzwans,
You are confusing line-of-sight with trajectory. Scope height changes your point of view (LOS). CANT changes the direction that gravity pulls relative to the gun-scope system. Gravity affects the pellet path, but not the LOS. High scope or low scope, LOS is unaffected.

broekzwans,
I await your mathematical proof.
Click to expand...
I think what we are talking about here is the effect of cant when shooting beyond (or below) your zero. If that's the case, the effect of scope height is indisputable when using some portion of your reticle to hold on the target. Am I missing something?
Click to expand...
Apparently, it IS disputable. Gun cant errors are independent of scope height. It can't be any other way.

Don't mix "scope cant" with "gun cant". They are two separate issues, though the symptoms are often mistaken for each other.

Scope cant is dealt with during mounting of the scope.
Symptoms manifest when shooting beyond (or inside) your zero apex. The more holdover/clicks, the worse the error. Fix by rotating the scope in it's mounts.

Gun cant is dealt with at the time of the shot.
Symptoms increase with distance from muzzle. The farther the target, the worse the error. Fix by holding the gun in the same horizontal/vertical reference that was used to establish the zero.
 
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@scotchmo, we are talking about a PROPERLY mounted scope on a gun that is canted due to operator error. The whole thread started with anti-cant devices that show the shooter if they are holding the rifle vertically or not. 

Improperly mounted (canted) scopes are not the point here. Given the context of this discussion, we are talking about canted RIFLES, and assumes that if the rifle is canted, so to is the scope. 

Are we on the same page yet? Phew! 

 
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"Brian.in.MI"@scotchmo, we are talking about a PROPERLY mounted scope on a gun that is canted due to operator error. The whole thread started with anti-cant devices that show the shooter if they are holding the rifle vertically or not. 

Improperly mounted (canted) scopes are not the point here. Given the context of this discussion, we are talking about canted RIFLES, and assumes that if the rifle is canted, so to is the scope. 

Are we on the same page yet? Phew! 





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Good. Canting a gun with a properly aligned scope (no built in scope cant). I wanted to make sure that was the only thing we are discussing here.

Then we are talking about trajectory only. As soon as the pellet leaves the muzzle, gravity starts to pull it down. When we sight in, we are angling the barrel slightly upward in order to give vertical compensation for gravity. If we also angle our barrel to the side (gun cant), what once was strictly an upward angle, now has two components: a horizontal shift, and reduced vertical compensation:

horizontal shift = drop x sin(angle)
vertical shift = drop x (1-cos(angle))

It does not matter if you were viewing the target from 2" above the barrel, or from 4" above the barrel. Once the pellet leaves the muzzle, gravity takes over. If gravity is not acting in the direction that you thought, you miss.

If you had sighted-in and were shooting in a zero G environment, gun cant would not be an issue.

 
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What is happens when you cant the rifle is the following:



To make my calculations easier to understand for everyone I assume that when I cant the rifle I cant around the axis of the bore, so bore is the center of rotation. To make it even clearer I take some exaggerated scope heights, so 2 cm above bore and 10 cm above the bore. For the rifle cant I take 5 degrees and for the distance I'm using 50 meters (which is also the initial zeroing distance). I'm using metric units because that's easier for me to use.

When I start canting my rifle the following thing happens to the alignment of the bore and scope:



The black dot is the center of the bore, the green dot is the scope placed at 2cm and the orange dot is the scope placed at 10 cm. The purple line is the new height of the scope above the bore (vertical) and the red line is the new horizontal misalignment of the bore.

The purple line can be calculated with the following formula:
height above bore * cos (canted angle)

The red line can be calculated with the following formula:
height above bore * sin (canted angle)


So for our two different scope heights:
2 cm with 5 degree cant -> new vertical distance (purple line) becomes 1.99 cm and the horizontal distance (red line) becomes 0.17 cm

10 cm with 5 degree cant -> vertical becomes 9.96 cm and horizontal 0.87 cm


For the next calculation I'm using the scope as center of rotation since your aiming at a fixed point, the calculated values above stay the same but we then assume the bore swivels under the center of the scope.



As you can see the horizontal misalignment will be magnified when increasing the distance. Now using chairgun I determine the first crossing point with the trajectory for both scope heights:

1.99 cm -> first crossing point is 5,5 meters
9.96 cm -> first crossing point is 15.8 meters

To calculate the misalignment on target the following is used:

2 cm -> 0.17 / 5.5 * (50 - 5.5) = 1.375 cm
10 cm -> 0.87 / 15.8 * (50 - 15.8) = 1.88 cm


As you can see the black line is longer than the green line (use Pythagoras and you'll see), on a very long distance the actual flight distance is longer than the sight distance which causes an extra vertical drop due to the bullet/pellet trajectory. For pellet ranges this is can be neglected.


With keeping the same 50 meter zeroing distance and shooting at 100 meters the error will grow linearly:

2 cm -> 0.17 / 5.5 * (100 - 5.5 ) = 2.92 cm
10 cm -> 0.87 / 15.8 * (100 - 15.8) = 4.64 cm




So to conclude some things that are debated above:

- gravity/trajectory doesn't come in to play at airgun distances (calculate the new flight distance vs uncanted flight distance and you'll see the extra distance is below 0.0001 %). If the extra distance would matter a higher placed scope will give less drop. Check chairgun for this, place you scope on two different heights and check at 100 meters, lets say 1 % extra due to cant will make the actual distance 101 meters. A higher placed scope will have less drop on the 1 meter extra than a lower placed scope.

- yes it already matters at the zeroing distance

- Larger canting errors/angles makes it worse
- Longer distance makes it worse
- Scope mounted higher above the bore makes it worse
 
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Thanks guys :) I'm an electrical engineering student so numbers is all I see all day :p
Is that your shooting location Brian? nicely covered in the woods!


But now I'm still looking for a bubble level that can be shipped to the Netherlands. I've had a scope attached swiveling wheeler but for some reason I didn't like the swiveling. Every time I openend it, it had a slightly different angle. The concept was nice though, it wasn't taking too much space and looked nice. Now every time I find a nice one I read that the company doesn't ship outside the US or the shipping cost is so incredibly high that it loses it value to me :( Maybe I'll go for the first degree accuracy one, some investment are for a lifetime, and since 34 mm scope tubes are getting more and more common here it'll never be wasted.
 
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@broekzwans,

When you cant the gun, while holding on target:

The bore line (dashed cyan line) is not the cant axis. NO

The parallel lines of the scope above the bore (dashed orange and green lines) are not the cant axis. NO

The cant axis is the line of sight to the center of the target (solid orange and green lines). YES

(trajectory compressed in x-axis to fit screen):
 
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"broekzwans"Thanks guys :) I'm an electrical engineering student so numbers is all I see all day :p
Is that your shooting location Brian? nicely covered in the woods!


But now I'm still looking for a bubble level that can be shipped to the Netherlands. I've had a scope attached swiveling wheeler but for some reason I didn't like the swiveling. Every time I openend it, it had a slightly different angle. The concept was nice though, it wasn't taking too much space and looked nice. Now every time I find a nice one I read that the company doesn't ship outside the US or the shipping cost is so incredibly high that it loses it value to me :( Maybe I'll go for the first degree accuracy one, some investment are for a lifetime, and since 34 mm scope tubes are getting more and more common here it'll never be wasted.
Click to expand...
Look in UK , France or Germany.
 
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"Scotchmo"@broekzwans,

When you cant the gun, while holding on target:

The bore line (dashed cyan line) is not the cant axis. NO

The parallel lines of the scope above the bore (dashed orange and green lines) are not the cant axis. NO

The cant axis is the line of sight to the center of the target (solid orange and green lines). YES

(trajectory compressed in x-axis to fit screen):
Click to expand...
I think I will have to produce a video using 2 different scope height with the same rifle. LOL
Different scope height cannot have the same results. NO.
 
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"GQ"
I think I will have to produce a video using 2 different scope height with the same rifle. LOL
Different scope height cannot have the same results. NO.


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As far as gun cant errors, they will have basically the same result. I said basically because there is a small change in the angle of the line of sight. But that angle is so small, it can be ignored. The difference between a zero height scope and a 10cm high scope is about .0002% discrepancy. Way less than any rounding error that you might use.

Please produce a video. If you want to see the maximum cant error, tip the gun on it's side (90 degrees cant). For comparison, do it with a 2cm high scope and then a 10cm high scope.

Let's say a gun's trajectory has 6" of pellet drop from the boreline before hitting the bullseye.
Cant the gun 90 degrees:

The pellet hits to the side exactly the drop value.
horizontal shift = drop x sin(angle)

6" x sin90 = 6" horizontal shift on target

And it will be low by the drop value.
vertical shift = drop x (1-cos(angle))

6" x (1 - cos90) = 6" of vertical shift downward

The scope height will have no measurable affect on the amount of cant error.
 
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"Scotchmo"
"GQ"
I think I will have to produce a video using 2 different scope height with the same rifle. LOL
Different scope height cannot have the same results. NO.


Click to expand...
As far as gun cant errors, they will have basically the same result. I said basically because there is a small change in the angle of the line of sight. But that angle is so small, it can be ignored. The difference between a zero height scope and a 10cm high scope is about .0002% discrepancy. Way less than any rounding error that you might use.

Please produce a video. If you want to see the maximum cant error, tip the gun on it's side (90 degrees cant). For comparison, do it with a 2cm high scope and then a 10cm high scope.

Let's say a gun's trajectory has 6" of pellet drop from the boreline before hitting the bullseye.
Cant the gun 90 degrees:

The pellet hits to the side exactly the drop value.
horizontal shift = drop x sin(angle)

6" x sin90 = 6" horizontal shift on target

And it will be low by the drop value.
vertical shift = drop x (1-cos(angle))

6" x (1 - cos90) = 6" of vertical shift downward

The scope height will have no measurable affect on the amount of cant error.
Click to expand...
Good.
Will see the results in real.
Regards
 
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"Scotchmo"@broekzwans,

When you cant the gun, while holding on target:

The bore line (dashed cyan line) is not the cant axis. NO

The parallel lines of the scope above the bore (dashed orange and green lines) are not the cant axis. NO

The cant axis is the line of sight to the center of the target (solid orange and green lines). YES

(trajectory compressed in x-axis to fit screen):
Click to expand...

I already see where our stories are mismatching. We're both right, we're just looking at it a different way. Maybe I had to write this clearer but the dots I've used in the calculation above are the start of the line of sight and the placement of the bore at that amount of cant. With the angling plots I'm looking at the tip of the muzzle towards the target.

Your story holds if the canting axis is right in between the two scopes, in that case the scope height doesn't matter and will give the same spread from canting. If we move the first scope to 1 cm and the second scope to 11 cm there is still no change. You're completely right in this!

If we look at three different swiveling points I think it'll be clear. In the following I've added an extra dot, a red one, this will depict the center between the two scopes. 

The first situation: center of my canting axis is the line of sight from the 10 cm scope



The second situation: the center of my cant axis is the center between the two scopes



For the record: added the 1 cm and 11 cm scope height into the picture for extra clarity

​


The third situation: The center of my cant is the line of sight from the 2cm scope





As you can see above, when we chose the center of the scopes as canting axis both scopes move an equal amount from the bore which causes no impact shift between the two scopes. If we look at the total displacement of the bore compared to the cant axis you can see that the horizontal barrel misalignment becomes larger with an increasing scope height.

For the record: I'm not trying to burn you or trying to be a smart ass, I'm just trying to get us on the same page ;)
 
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