Optimal scope height study



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Offline Scotchmo

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Re: Optimal scope height study
« Reply #40 on: November 21, 2018, 03:53:00 PM »

With greater distance between the bore and the line of sight, does it not move the rifle further laterally from the line of sight at a given amount of cant?

No. You are still aiming at the same point.
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Offline Motorhead

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Re: Optimal scope height study
« Reply #41 on: November 21, 2018, 04:01:46 PM »

With greater distance between the bore and the line of sight, does it not move the rifle further laterally from the line of sight at a given amount of cant?

No. You are still aiming at the same point.

That makes no sense .... If the bore is ABSOLUTELY under the Cross hair on the vertical plane we have no cant .. this a given.  As the distance between bore C/L and Scope C/L increase, so increases the horizontal shift distance for the same amount of cant angle.

Now that said I'm admittedly NOT an engineer and schooled in angles / trig & such   :-[
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Offline Scotchmo

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Re: Optimal scope height study
« Reply #42 on: November 21, 2018, 04:07:01 PM »
Pretty sure this is true and the "why for" of my statement .. just the slightest cant the POI  much more so shifted sideways much greater than the same cant dd with my more typical  lower "hunter scope height"
Either that or I'm nutz

You're "nutz"  ;D -

Scope height does not enter into the equation. Itís strictly a function of pellet-drop and cant-angle.

horizontal shift = drop x sin(cant_angle)

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

If you plot the cant errors at all angles, you get this:


The pellet could care less how high your scope is mounted. It will go where it's pointed.

A "what if" experiment (just think it through - no need to actually perform a physical experiment):

You have one gun with two scopes mounted on it. One at 2" high and one at 6" high. Both scopes are zeroed at 50 yards. Lock the gun down in a bench rest aimed at a 50 yard target, while also canted 30 degrees to the right. The gun will not be moved for the entire test. You can look through either scope and see the crosshair on the bullseye. Fire a pellet at the target without looking through the scope. Then do it while looking through the 2" high scope and also while looking through the 6" high scope. It will hit right and slightly low. At the same point POI, every time.

It does not matter which scope you are looking through, or how high it is mounted. The amount of gun cant error is determined by the amount of drop and the degree of cant. It "can't" be any other way.

Trigonometry and geometry are two of my specialties. Calculus - not so much. This is a fairly straightforward geometry/trig problem, where the result can go against one's intuition.
« Last Edit: November 21, 2018, 04:19:38 PM by Scotchmo »
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Re: Optimal scope height study
« Reply #43 on: November 21, 2018, 04:23:40 PM »
Thank you Scott ... so my guess is that while shooting WFTF, the difficulty in maintaining "Level" is whats killing me.  When shooting hunter I live & die by my level and always paid MUCH attention to it prior to each shot.

I'll stay with nutz ... 60 years now it has served me pretty well  ;D
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Offline Bryan H.

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Re: Optimal scope height study
« Reply #44 on: November 21, 2018, 04:26:06 PM »
Brother that is a great illustration, but where is height over bore taken into consideration?  Also, since when do you take all of your shots at the same range you are zeroed from?

It is hard for me to sit in my chair and question someone like you on that, but it definitely makes a difference.  Especially in closer or our further than your PBR.

And with 6" height over bore?  Vs 2.5"?? That doubles the distance of poa from poi.  No way that it doesn't matter.  Might not be as big a deal at the range you are zeroed, but for sure it will matter at different ranges.

And finally,  I have fired a lot from odd and awkward positions in my life.  I can tell you for a fact, if you have to shoot laying on your side, your POI changes drastically.

All I am trying to say is, height over bore matters, relative to the angle of the shot. For sure it mattere outside of your PBR and matters more as the amount if cant increases.
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Offline Scotchmo

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Re: Optimal scope height study
« Reply #45 on: November 21, 2018, 06:25:32 PM »
Brother that is a great illustration, but where is height over bore taken into consideration?  Also, since when do you take all of your shots at the same range you are zeroed from?

It is hard for me to sit in my chair and question someone like you on that, but it definitely makes a difference.  Especially in closer or our further than your PBR.

And with 6" height over bore?  Vs 2.5"?? That doubles the distance of poa from poi.  No way that it doesn't matter.  Might not be as big a deal at the range you are zeroed, but for sure it will matter at different ranges.

And finally,  I have fired a lot from odd and awkward positions in my life.  I can tell you for a fact, if you have to shoot laying on your side, your POI changes drastically.

All I am trying to say is, height over bore matters, relative to the angle of the shot. For sure it mattere outside of your PBR and matters more as the amount if cant increases.

"...great illustration, but where is height over bore taken into consideration?..."

It's not taken into consideration because scope height does not enter to the equation for pellet drop. From where you choose to spectate the shot does not affect the pellet path.


"...Also, since when do you take all of your shots at the same range you are zeroed from?..."


My POA (Point Of Aim) always matches my intended POI (Point Of Impact). It does not matter if I'm clicking to rezero, or if I'm using a different mil-dot as my "zero". A stadia type reticle has multiple aim points, therefore multiple zeros.

Here is a special situation, and maybe it is what you are talking about:

Aiming high vs using your mil-dots or clicking

Let's say that you are shooting at a very close target. But all you have is a target dot reticle (only one zero point). You are going to make the shot without clicking. You will need significant "holdover". In this special instance, you will not be aiming at the bullseye, you will be aiming above the target. For a low scope, the POI might be 1" below the reticle dot. For a higher scope the POI might be 2" below the reticle dot.  You will aim 1" above the bulleseye when using the low scope, and 2" above when using the high scope. And that will work. But now let's also say that the LOS (Line Of Sight) is canted 30 degree for both shots. Canting now includes an additional error that is related to scope height. You will get the drop related cant error (from gravity), but you will also get a LOS error. Your POA is now canted with respect to the bullseye, so you will get an additional error directly related to scope height. For a close target, the high scope will produce more error. For far targets, it's less of a problem. But for those far targets, the lower scope will have slightly more error. This additional error does not care about pellet drop, it cares about POI from trajectory apex.

If you click, or use "holdover" points on the reticle, than scope height does not determine the degree of cant error. However, if you aim for a higher point on the target (not the bullseye), you are also canting the LOS, so you will have two types of cant induced errors present. Gun cant AND LOS cant.
« Last Edit: November 21, 2018, 06:31:06 PM by Scotchmo »
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Offline nced

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Re: Optimal scope height study
« Reply #46 on: November 21, 2018, 07:36:16 PM »
Brother that is a great illustration, but where is height over bore taken into consideration?  Also, since when do you take all of your shots at the same range you are zeroed from?

It is hard for me to sit in my chair and question someone like you on that, but it definitely makes a difference.  Especially in closer or our further than your PBR.

And with 6" height over bore?  Vs 2.5"?? That doubles the distance of poa from poi.  No way that it doesn't matter.  Might not be as big a deal at the range you are zeroed, but for sure it will matter at different ranges.

And finally,  I have fired a lot from odd and awkward positions in my life.  I can tell you for a fact, if you have to shoot laying on your side, your POI changes drastically.

All I am trying to say is, height over bore matters, relative to the angle of the shot. For sure it mattere outside of your PBR and matters more as the amount if cant increases.
My experience shooting .177 cal HW springers (HW95 & Beeman rebadged R9) tuned to shoot at from 12.5 to 13.5fpe is that scope height above the bore does affect the point of impact at different ranges. When using "hold over aiming" with a 30 yard zero a scope close to the receiver the "trajectory flat spot" happens at closer ranges, however if the scope is higher above the receiver the  "trajectory flat spot" happens at the longer ranges. Here is an example of the "trajectory flat spot" (distance between the near and far zero) of a tune for my .177 R9 done a while back...........

Notice that using a 30 yard zero and scope about 1 3/4" above the bore I had a "trajectory flat spot" of about 13 yards to 35 yards. This was when I was using a 3-12x40 Vortex Diamondback scope set in medium height mounts.

For a while now I've been using scopes with 50mm objectives so I've needed high mounts so the front bell would clear the receiver and have noticed that I have more issues hitting close targets on the FT course that I did when using medium mounts with 40mm front bell.

Offline Scotchmo

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Re: Optimal scope height study
« Reply #47 on: November 21, 2018, 08:55:17 PM »

My experience shooting .177 cal HW springers (HW95 & Beeman rebadged R9) tuned to shoot at from 12.5 to 13.5fpe is that scope height above the bore does affect the point of impact at different ranges.
...
For a while now I've been using scopes with 50mm objectives so I've needed high mounts so the front bell would clear the receiver and have noticed that I have more issues hitting close targets on the FT course that I did when using medium mounts with 40mm front bell.

Ed,

No one is arguing that point. I think everyone knows that the difference between POI and drop varies depending on scope height. That would be a vertical dispersion.

A high scope will increase the amount of vertical error when you mis-range a close target. But that high scope won't increase the amount of error caused by a specific gun cant angle.

Bryan was arguing* about the scope height as related to cant angle. That is primarily a horizontal dispersion. I am arguing* that scope height has no bearing on gun cant angle.

* When I say arguing, it is in the good sense of what's needed for a productive resolution to any subject that is being debated.
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