Home Forums Hunting & Shooting Ask The Gunwriters Ask John Barsness Questions About "SCOPE HEIGHT."

I discovered the same thing many moons ago but but my fix instead of higher scope rings was more drop in the stock.

Terry

Excuse me John but the article contains an error. This is not your fault because it is a common myth about the scope height. In reality the canting error does not depend on the scope height, only on the canting angle and the bullet drop at the given distance which can be proved very easily anyway.
Cheers, Andras

Andras,

I would appreciate your explanation of that easy proof.

My understanding of cant is that the higher the scope, the farther the bore lies from the vertical line of sight, given a certain angle of cant. The increased distance from the line of sight creates more error in the bullet's trajectory.

It will be interesting to hear why this isn't so.

I remember reading in RIFLE, I think, a while back about someone shooting one of JOC's rifles and commenting that the crosshair was in the upper right hand corner. While centered is nice it sure didn't keep him from harvesting game with an off center reticule.

Yeah, a centered isn't nearly as critical as some of us think.

That said, there's a big difference between crosshairs that ended up WAY over against the edge of the view, and those in the early Leupold Vari-X's, which wouldn't move very far off center.

Completely agree, I certainly wouldn't want to go back.

Antiquated rocket science. My 30+ year old Vari-X II's stumble through it...

Hi John,

I'll explain it with pleasure, this is why I've registered on this forum. I'm also a shooter anyway but with air rifles (Field Target).

The shots from a canted rifle will impact along an arch, and the displacement of the pellet impacts depends only on the angle of the canting and the pellet drop at that distance (relative to the bore line).

The height of the scope has nothing to do with this. Why? It's proven by tests by J. Hogema and can be proved theoretically, too: if you aim at a point, the bore line looks with 'd' above (d is the bullet drop) so the bullet which drops 'd' can hit the target. If you rotate the rifle but still looking at the target, the bore line will draw a circle around the target with this radius 'd' and the impact will be always with 'd' vertically below this circle, independently from the scope height.

For the very easy explanation, why scope height doesn't affect the canting error, please have a look at the picture below:



Simply imagine a rifle with more scopes mounted on it, one above the other. Each scope is zeroed at the given distance, each sight line looks at the same point, where the gun will shoot. If you cant the gun with an angle, you might aim through any of the scopes, lower or higher, they look to the same point, the gun underneath will be in the same position too, so the canting error will be the same. The canted shots move along a circle and the amount of displacement depends only on the pellet drop (d) and on the angle of canting (a). It doesn't matter how high your scope is, you always have to pay the same attention to avoid canting the rifle.

Best regards,
Andr�s

JB, read the 'proof'.

Another example as mentioned on another thread, 'Formula Heavy'.

All I can say is it's probably a good thing we can apply 'cant' to rifle sight's height,.......in a circle.

That theory may may true at the exact distance that bullet impact and point of aim coincide. Move the target closer or further away, and I suspect there will be error. I think that "Kentucky elevation" would be somewhat less effective, when scope cant is introduced.

Jeff

Yeah, now I'm going to have to run some more tests, since formulas don't pack it when writing for magazines!

On the other hand, it's probably worth at least one article....

I must have been really lucky all these years to hit anything without access to that chart!
Interesting,though.

Jeff,

Aim point and impact point always do coincide - assumed that the rifle is zeroed properly. It doesn't matter that you set the scope with clicks or use one of the mildots to aim for different distances, the LOS will always look at the target and the barrel will look always with 'd' above in order to hit the target ('d' is the bullet drop relative to the barrel at the given distance). It's quite logical, ain't it?

Anyway, I've tested it, too. With an air rifle a small scope mounted on 2.5 cm CTC and then with another scope with risers at 10 cm. Zeroed both times then rotated with 45 and then 90 degrees, the canting error was the same for both scope heights.

It's another interesting question that if you don't know the distance and under/overestimate it, the canting error can increase or decrease (related to the precisely zeroed rifle), or even be fully eliminated. It can even happen that your POI is tragically low but remains on the same place with any canting...

John,

This is a very good idea, please try it - with the same rifle&bullet of course - with a very low and very high mounted scope. Zero the scope in both cases and then rotate the rifle with 90 degrees. You will find that the canting error will be the very same (exactly the 'd' anyway to the side and down as well).

The only thing you shall be aware of is that the 'd' value has to be much bigger than your own inconsistency. If you shoot at 50 yds with a big bore rifle then you can't really use the results. Use a small bore rifle with low-powered bullets.

Yes I'm going to write an article about it to our FT forum because many people have this misbelief and I don't blame them because it seems to be very logical at first glance but facts are facts.

I'm looking forward to seeing your test results.

Well, now you've gone and dunnit, MM.
You can bet there will be at least one, perhaps two, shooters in Montana checking this out....
The arc-of-bullets phenomenon is well shown to anyone who cares to try it, which is why I mount everything I can as close to the bore as I can. AND put a level on.
The article itself is sort of an interesting flashback to one of Ken's articles about scope height and the fatter "point-blank" you get, a few extra yards -- but I've never been in quite the shooting where raising the scope would be a consistent benefit. I take clicks or hold over.

m_m

Interesting stuff! My curiosity is definitely piqued. Look forward to seeing what JB comes up with. If winter ever ends here, I'd like to try it out, as well. This sort of thing is way more interesting than the soap opera that this forum has turned into! Thanks for posting.

Jeff

I'm going to test it again sometimes with an air rifle (about 5 cm drop at 20 metres so the canting error is easy to see), fully documented etc., I'll let you know the results.

And I'm going to test it with a centerfire at 100 and 200 meters.

John,

This chart may help you out, I did this myself a few months ago...

Thanks very much, Kirk!

How much are you asking for reprinting rights?