Rifle scopes - Level or not?

You can buy offset scope mounts:
http://ultimak.com/pic36.htm

M1C & M1D Garands used them... well, not that offset.

acm said:
2. If your scope isn't mounted level, but you hold the crosshairs level, you're only going to get one zero, and your windage error is going to increase with distance because you have to shoot ACROSS your line of sight for that first zero because of the horizontally offset bore.

Am I missing something?
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That is correct, the image above is conceptually right. However, what they are trying to get across is that the error in practical terms is not significant.

It can be worked out with simple trigonometry. Here is a table of what that error looks like with a typical height for a scope with a very large objective:

Cant.jpg


Here are different lines canted at different angles:

line.jpg


How much cant are you realistically going to have? 5 degrees is VERY noticeable. Even 2 degrees cant can be detected with the naked eye fairly easily. Realistically, 3 degrees of cant is a lot to have... and your offset is a mear 1.036" or 0.10 MOA at 1000 yards (I didn't use exact MOA in the calculations, btw). That gets lost in all of the other noise, in practice.
 
How about this?

Shoot a group a 100 with your nicely leveled scope and your most accurate rifle, then crank 30 minutes of elevation into it and do it again. Hopefully they stack 1 directly above the other.

Put your scope on crooked and repeat the process. Use level crosshairs in either case. Don't use use theory, trig, last month's match results or the solunar charts, just a handful of cartridges and a plumb bob.

Report the result. I double dog dare ya.:p

Scope horizontal errors while vertical tracking can be remedied by rotateing the scope, this is well known and proveable. It follows that they can be induced the same way.
 
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My pic was an extreme example as I said just so you can visually see the difference.

I spent 2 minutes to make the pic in to counter this post

"There are many different scenarios being presneted here, and not eveyone is on the same page.

The sights do not need to be in any set position. They can be as close or as far away from the rifle as you want. The important part is that the relationship between the sights and the rifle must be maintained from zero/sighting in, to actual shooting.

For simplicity, sights are usually mounted on top. This makes plumbing up and adjustment very linear, parallel, and easy.

This seems like an problem that would be easier to understand with an illustration. Words just aren't cutting it."
 
People still seem to be confusing two different different scenarios. Rotating the scope fixes the problem when you're leveling the rifle relative to the target with the scope canted. If you've leveling the scope relative to the target, you wouldn't see the problem to begin with. These are different.

Science and math never appeals to those who can't grasp them. That's a nice little experiment above, but those who are actually grasping the difference between the two situations will realize that cracking your elevation up 30 minutes isn't going to change a thing. You'll definitely see sideways movement of the group if it's the rifle that is level and not the scope. I'll take the theory and the trig over the experimental results of someone who can't grasp them any day. Their results are likely useless because they're full of errors due to things like not understanding the difference between leveling the rifle and leveling the scope when the scope isn't plumb with the rifle. Which did they actually do in the experiment? Who knows? ...they clearly don't.
 
Wow! Are the emotions running high?
Hi Dogleg, good to hear from you!

To all guys who responded to this thread posting:
There is allot of very accurate/truthful statements here!
The hardest part about a technical problem, is to explain it in a way that "everyone" aggrees with it.
Its my observation that there is allot of shooters out there that dont understand this subject matter in detail, and they shoot fine.
Like in most instances, problems are accumulative. The greater the missalignment the worse the problem. Just do your best to align all three components, and enjoy the result.
If it doesnt work, try again.
I am not the most experienced shooter "beyond 1000 yds."
But i have successfully shot out to 1900 yds multiple times.
And after all that shooting, I noticed one day that my crosshairs/rifle/sope bubble level/ really wasnt super well aligned! Kind of embarressing? Nope, because I can make mistakes, and correct them.
I made my adjustments, and everything was "still just fine".
If this alignment issue is so critical, I wouldnt have been able to shoot as well as I did before the corrected misalignment. At least that is "MY personal interpretation".

I know for myself, the better I feel about my set up, the betrer I tend to shoot.
Have fun guys and dont fret about others not aggreeing with your methods or approach to a subject. I have that problem sometimes too.
 
a few degrees of cant, even out to 500+yards with a 100 yard zero won't make any significant change. but it will cause some lateral offset at varying distances. If the difference is 1/8" at 300 yards that could be a bullseye, or just far enough out. I like to eliminate all mechanical problems and just lave myself as the bad link in the chain
 
You will never know if you have truly eliminated the cant (or any small horizontal offset, for that matter) between the scope and the axis of the bore because as long as your scope is level, it will track vertically at a given distance if you box test it. The small offset will be lost in things like group size and wind. Take several rail mounted levels and put them on the same rail. It isn't uncommon for them not to all read level at the same time (flop-out levels are notorious for this). Do you know that the top of your rail is truly perpendicular to the axis of the bore? Maybe on a one piece custom action. On a mass-produced round action with a screw-on rail, not so much... How about the rings? Is there any horizontal offset in those? Maybe... They also usually only clamp on one side. If the rail is thicker or thinner than nominal, there will be horizontal offset. None of this matters, as long as the level shows you when the scope is level, it's going to track vertically and you won't be able to detect any of this when shooting at one particular distance because what that cant contributes horizontally is a constant in the equation.

The point here is that when you install a level, be it scope mounted or rail mounted, you always rotate the level or the scope so that the bubble levels the internal axis of adjustment of the scope (the cross-hairs may not even be plumb with this, especially on cheap scopes). Trying to get things level with the scope rail, scope body, turrets or anything else may give you a good feeling, but it really isn't solving anything. Canting the scope itself is the thing you're trying to avoid. Box testing will only show that you that the scope is level when the bubble is centered.
 
Injundon, i understand where you are coming from. Take absolutely EVERY variable out of the equation possible. Thats sound judgement.
That will make everyone shoot better.

But as always, the shooters that score the highest on average, will have more control of the environmental factors.
A gun thats shoots to its potential, shot by an average wind doper will shoot well.
A gun that shoots as good as most of us gunnutz can tune it(shot by a great wind doper) will kick butt.
I promise you that the best shooters/wind dopers, can shoot "all" of my rifles better than I can, reguardless of the level of perfection my scope/rifle/scope level is tuned to.

In the end of all this, you have to be content with your set up.

My scope alignment issue is "relatively" important to me, but I would rather expend most of my energies shooting, and learning to dance with the hardest, uncontrolable variable, "the wind".
Thats were I have lots to learn!
 
....Take absolutely EVERY variable out of the equation possible....
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Except some things are not variables, even small variables, and so they don't matter (as far as accuracy goes) and they may be safely ignored or neglected.

If the forestock of my rifle is painted red and the buttstock is black - that is an inconsistency, and I could make things "more consistent" by painting all of the rifle red, or all black. But the truth is it doesn't matter what colour which parts of your rifle are, the accuracy is unaffected. There might be other good reasons to paint your rifle nicely, for example it might look better - but there is no *accuracy* reason to fuss about this.

We shooters are willing to do anything and everything it takes to shoot well. It seems to me that there are probably a hundred different things to do or to pay attention to, w.r.t. rifle setup, shooting, and reloading. And I am reasonably certain that of those 100 things, 70 of them probably do not matter at all, not one little bit. The problem is, how do we know which one? It's usually easier to simply _do_ all of the hundred things that various successful shooters do, rather than expending the effort on a private research program to find out which ones are useless and can be ignored. So it is nice to be able to find the odd thing that you can truly, knowledgeably dispense with.
 
I'm way too fussy to not plumb my scope and rifle. I want my vertical adjustments to be vertical, not up and to the side. If I'm dialing a scope up for an 1200 yard shot at a coyote I don't want to have to worry about making a windage adjustment because I was too lazy to install the scope properly in the first place. It probably ends up being a small amount of correction, but zero adjustment is better than any other adjustment.
 
BigUglyMan said:
I'm way too fussy to not plumb my scope and rifle. I want my vertical adjustments to be vertical, not up and to the side. If I'm dialing a scope up for an 1200 yard shot at a coyote I don't want to have to worry about making a windage adjustment because I was too lazy to install the scope properly in the first place. It probably ends up being a small amount of correction, but zero adjustment is better than any other adjustment.
Click to expand...

That's the way I look at it too. It doesn't take that much more time, you may or may not gain any benefit from it (according to the various responses), but it certainly won't hurt anything. Great debate guys, who knew it could get so heated :)
 
The reason I level my scope is because I want one adjustment (elevation) to be parallel to the force of gravity. I don't really want to start having to do trig and adjust two different settings to make a range adjustment.

You can also fly an airplane straight with the wings canted 10 degrees to the horizon. It's just more difficult. Which is why we don't do it much.
 
You know, a lot of guys who seem to obsess about "leveling" their scope seem to equate that with leveling the cross-hairs or aligning them to something on the rifle. It is possible to have cross-hairs that are not plumb with the adjustments. It's also possible to have turrets with clicks that aren't exactly what they're supposed to be. That's more likely to happen in cheap scopes, but I've seen them in a few high-end ones too.

A savvy shooter will box test his setup to make sure that the scope not only tracks vertically and horizontally, but that the turret adjustments are also accurate. It's surprising how few seem to do that, but assume everything to be "level" because they aligned the cross-hairs to some "golden" surface or edge.
 
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