Rifle Cant With Level Scope, Fact Or Fiction?

[Vamike9]

I've read several articles on this topic, yet I want to know what you all think about this? I've seen real world tests done that explain that you can have your rifle canted but have a scope level with gravity and make long-range precision hits on target. Is this what you all see with your real world experiences in long range hunting? So is this a myth that you have to have your scope completely level with your rifle to make good hits at long range?

 

[FearNoWind]

... I've seen real world tests done that explain that you can have your rifle canted but have a scope level with gravity and make long-range precision hits on target....

You can hit an intended target with a canted rifle. To do it with "precision" as in repeatable X ring groups is another story. But ... you've got to adjust the scope to account for the cant angle. When you fire the rifle a bullet exits the muzzle. The relationship between the various elements (muzzle relationship to the target, how the rifle's recoil affects muzzle movement and applicable ballistics data) determines where the bullet will go. Theoretically, you could roll the rifle over on its side and still hit a target, with some degree of accuracy, using the scope to line up the shot. But you'd have to know how to accommodate all of the physics involved.
Consider this. You can fire a rocket into space toward the position that the moon will be in when the rocket arrives. But, in the interim, the rocket's trajectory will not be in direct alignment with the moon's position.
All that being said, forget about hunting with a canted rifle. The results will not be what you expect based on a properly aligned rifle and scope.

 

[ELR Researcher]

I've read several articles on this topic, yet I want to know what you all think about this? I've seen real world tests done that explain that you can have your rifle canted but have a scope level with gravity and make long-range precision hits on target. Is this what you all see with your real world experiences in long range hunting? So is this a myth that you have to have your scope completely level with your rifle to make good hits at long range?

Learned long ago that it is easier to understand such issues if you exaggerate the variable - since its easier to visualize and your looking for the effect of any change in the variable.

Assume a rifle cant of 90 degrees (my exaggeration for this discussion). The vertical distance between the centerline of the barrel bore and the centerline of the scope is now zero. Yes, you can make a hit but the POI will have moved (if you were still using the same POA) - how much depends on the distance and actual projectile ballistics given the load and specifics of the platform.

For the questions not asked:

Yes, its worth while correcting for the cant before pulling the trigger. And, yes, its worthwhile having and using a good, properly installed, cant indicator and properly aligned scope.

 

[Vamike9]

Ok, thanks for the information everyone. Hopefully these answers will help others understand this as well.

 

[jimbires]

these two articles explain this pretty good . maybe these will give you a better understanding . hope it helps .

How Canting Your Rifle Affects Long Range Accuracy



Reticle Perpendicularity

 

[J E Custom]

You can hit an intended target with a canted rifle. To do it with "precision" as in repeatable X ring groups is another story. But ... you've got to adjust the scope to account for the cant angle. When you fire the rifle a bullet exits the muzzle. The relationship between the various elements (muzzle relationship to the target, how the rifle's recoil affects muzzle movement and applicable ballistics data) determines where the bullet will go. Theoretically, you could roll the rifle over on its side and still hit a target, with some degree of accuracy, using the scope to line up the shot. But you'd have to know how to accommodate all of the physics involved.
Consider this. You can fire a rocket into space toward the position that the moon will be in when the rocket arrives. But, in the interim, the rocket's trajectory will not be in direct alignment with the moon's position.
All that being said, forget about hunting with a canted rifle. The results will not be what you expect based on a properly aligned rifle and scope.

+1

In simple terms, If the rifle is canted and the scope is level, when you change distance you will have to adjust both the elevation and the Windage to be spot on.

J E CUSTOM

 

[el matador]

Having the scope nice and plumb when you shoot is by far the most important thing. Line up your reticle with a plumb line, zero your scope level, and tighten her down. Do a tall target test to verify your elevation adjustment is tracking as it should.

Here is the amount of windage error you can expect at 1000 yards if something isn't perfectly aligned:

Scope is plumb, gun is canted 5 degrees: 0.7"
Scope is plumb, gun is canted 10 degrees: 1.4"
Scope is aligned with gun, both are canted 5 degrees: 21.9"
Scope is aligned with gun, both are canted 10 degrees: 44.1"

 

[ajridgedell]

Having the scope nice and plumb when you shoot is by far the most important thing. Line up your reticle with a plumb line, zero your scope level, and tighten her down. Do a tall target test to verify your elevation adjustment is tracking as it should.

Here is the amount of windage error you can expect at 1000 yards if something isn't perfectly aligned:

Scope is plumb, gun is canted 5 degrees: 0.7"
Scope is plumb, gun is canted 10 degrees: 1.4"
Scope is aligned with gun, both are canted 5 degrees: 21.9"
Scope is aligned with gun, both are canted 10 degrees: 44.1"

I would like to know how this is calculated. Its seems to me it would be dependent on how much elevation you dial into your scope.

 

[el matador]

I would like to know how this is calculated. Its seems to me it would be dependent on how much elevation you dial into your scope.

The top 2 numbers are only dependent on the horizontal offset of the scope with respect to the bore. That amount of offset will be the amount of error you get at each multiple of your sight-in distance. So if you have .25" of offset and zero at 100 yards:

At muzzle: -0.25"
100 yards: 0"
200 yards: 0.25"
300 yards: 0.5"
1000 yards: 2.25"

Those numbers get pretty insignificant with a 200 or 300 yard zero.

The bottom 2 numbers are dependent on your own bullet drop/elevation. Take the bullet drop at a given range and multiply by the sine of the cant angle. The example I used had 250.2" of drop at 1000 yards:

250.2 * sin5 = 21.89

The elevation would also be affected, but varies with the cosine. That is a fairly insignificant amount compared to the windage:

250.2 * (cos5 - 1) = -0.95"

So you'd hit 1" low and 22" right or left, whichever way you're canting.

 

[ajridgedell]

The top 2 numbers are only dependent on the horizontal offset of the scope with respect to the bore. That amount of offset will be the amount of error you get at each multiple of your sight-in distance. So if you have .25" of offset and zero at 100 yards:

At muzzle: -0.25"
100 yards: 0"
200 yards: 0.25"
300 yards: 0.5"
1000 yards: 2.25"

Those numbers get pretty insignificant with a 200 or 300 yard zero.

The bottom 2 numbers are dependent on your own bullet drop/elevation. Take the bullet drop at a given range and multiply by the sine of the cant angle. The example I used had 250.2" of drop at 1000 yards:

250.2 * sin5 = 21.89

The elevation would also be affected, but varies with the cosine. That is a fairly insignificant amount compared to the windage:

250.2 * (cos5 - 1) = -0.95"

So you'd hit 1" low and 22" right or left, whichever way you're canting.

Ahh.. I was having trouble understanding the first two, but I get it now.

 

[4xforfun]

These numbers you have here is based upon NOT adjusting your reticle for the shot. These numbers do not apply when you dial up your scope for that 1000 yard shot....which is EXACTLY what you will need to do.

 

[el matador]

These numbers you have here is based upon NOT adjusting your reticle for the shot. These numbers do not apply when you dial up your scope for that 1000 yard shot....which is EXACTLY what you will need to do.

It's not very complex geometry here. The error will be the same whether you're using hash marks on your reticle or dialing for elevation.

There is a small amount of error in my numbers due to sight-in distance and scope height, but I wasn't looking for a precise solution. I was only trying to show the magnitude of error that is introduced when the scope is canted. For exact windage and elevation error you need to know the divergence of the bullet from the center line of the barrel, which could be obtained from time of flight.

The Cliff Notes version is: The scope reticle is by far the most important thing to level.

 

[BergerBoy]

I just went through the pain in the *** of doing this to all my long range rifles. I like a plumb line or plumb-bob method. I have found that levels, even good ones are not as accurate as when you align your reticle with the plumb line after you have your rifle level. The biggest problem I found was that there are really no completely level places to set a level on most rifles. I set a level on my pic. rail but they all had a slight twist to them from the rear to the front. So what do I use? The reads off the front? Back? I just split the difference and place the level in the middle of my rail(chamber) - got it level, locked it in and then put the scope on it and aligned the vertical cross hair to the plumb-line and slowly tightened it up.

So to answer your question: YES, it matters... and it matters more the farther you shot.
JMO

 

[EXPRESS]

Some people can see plumb better than others, and some terrains can trick us all.

Personally, I'm no good with spotting plumb, so I use one. However, my error is repeatable, so I have shot without one, forcing myself to shoot at a "crooked" reticle.