Rifle scopes - Level or not?

[green machine]

rnbra-shooter
Big Mouth

Originally Posted by injundon
from the pic Im pretty sure your score is about 2 degrees off level bottom kicking to the right /Quote

FWIW this will have no effect on the rifle's accuracy nor on its point of impact.

The only need to mount a scope vertically is that it can look a bit silly if it is noticeably crooked.


08-12-2011, 06:41 PM #20
green machine
Newbie

FWIW this will have no effect on the rifle's accuracy nor on its point of impact.

The only need to mount a scope vertically is that it can look a bit silly if it is noticeably crooked.[/QUOTE

Definitely should be plumbed. If it isn't square to your action at distances other than zero it will be off to one side when holding over on mildots or clicking turrets. On my airgun field target rifle, I have a level mounted on the action just to make sure that
The rifle is in the same orientation for each shot. Level your action on a rest, then turn your scope in the rings so the vertical hair lines up with a weighted string you hang at around 20 yards. I promise this will help at long distance.


08-12-2011, 06:57 PM #21
rnbra-shooter
Big Mouth

The scope does not have to be mounted level/plumb to the action. It can be rotated, even by a lot (15 degrees, 30 degrees etc).

Shooting with the scope in the same orientation, preferably level, shot after shot is important (vitally important at long range). One can get a bubble level that attaches to a scope's tube for this purpose, also front sights for long range competition iron sights rifles are available with built in bubble levels.



08-12-2011, 07:11 PM #22
injundon
Newbie



Posts: 16 I've always just centered it to the center of the bolt screw.


08-12-2011, 11:12 PM #23
green machine
Newbie

Quote:
Originally Posted by rnbra-shooter
The scope does not have to be mounted level/plumb to the action. It can be rotated, even by a lot (15 degrees, 30 degrees etc).

Shooting with the scope in the same orientation, preferably level, shot after shot is important (vitally important at long range). One can get a bubble level that attaches to a scope's tube for this purpose, also front sights for long range competition iron sights rifles are available with built in bubble levels./Quote

If your scope was turned say 45 degrees right, then 4 clicks up @ 100 yards (one inch) would yield a change of impact point of .707 up and .707 right. Factor that in with the fact that gravity acts in a downward vector, you end up with a complicated curved trajectory. Simple physics. I have also seen this proved practically as well. Shooting with the scope plumb to the action helps with keeping the gun level, not canted, which gives you a misleading adjustment as earlier. Plus it only takes an extra 2 minutes, so why not try and gain every advantage available?



08-13-2011, 11:34 AM #24
rnbra-shooter
Big Mouth

green machine I understand your explanation and agree with your math. What you say is true, if you shoot with the rifle level and your scope canted 45 degrees to the right.

Look at the situation from a different angle - so long as the _scope_ is level when you aim and shoot, it does not matter what the rifle's orientation is w.r.t. it. If you make the scope level by (say) aligning the crosshairs with the horizontal and visual cues provided by a level/square target, or if you use a bubble level on your scope, it matters little if any just where exactly the rifle barrel is hanging w.r.t. the scope.

The point I was trying to make is that it is not at all necessary to fuss with a scope's orientation, for accuracy reasons. It is worth fussing with the orientation for reasons of cosmetics, or for reasons of rifle fit (sometimes a target rifle will fit a shooter well when it is in a canted position; in this case one can shoot with the rifle in the canted position, if the sights are oriented so as to be vertical when the rifle is in the chosen shooting position).

My main message - what matters is that the *sights* be aligned with the target.


08-13-2011, 09:51 PM #25
green machine
Newbie

Quote:
Originally Posted by rnbra-shooter
green machine I understand your explanation and agree with your math. What you say is true, if you shoot with the rifle level and your scope canted 45 degrees to the right.

Look at the situation from a different angle - so long as the _scope_ is level when you aim and shoot, it does not matter what the rifle's orientation is w.r.t. it. If you make the scope level by (say) aligning the crosshairs with the horizontal and visual cues provided by a level/square target, or if you use a bubble level on your scope, it matters little if any just where exactly the rifle barrel is hanging w.r.t. the scope.

The point I was trying to make is that it is not at all necessary to fuss with a scope's orientation, for accuracy reasons. It is worth fussing with the orientation for reasons of cosmetics, or for reasons of rifle fit (sometimes a target rifle will fit a shooter well when it is in a canted position; in this case one can shoot with the rifle in the canted position, if the sights are oriented so as to be vertical when the rifle is in the chosen shooting position).

My main message - what matters is that the *sights* be aligned with the target. /Quote

Definitely agree on the sights aligned with the target
But take my previous example, turn the entire rifle so the crosshairs are level, now the barrel centerline is to the right. It will be over (scope height/ sin cant angle) say for the example a scope height of 1.5 inches so (1.5/sin45)=1.06 inches. Picture that the line of sight and the line of sight through the barrel intersect, making two sides of a right triangle.that triangle will be rotated 45 degrees around the axis of the line of sight. If you stick a laser in the muzzle, and adjust it so it is zeroed at 100 yards, it will print on paper 1.06 right and 1.06 down at 0 yards, and 1.06 left and 1.06 up at 200 yards. Admittedly this is a simplified example with a laser. Throw in the arced trajectory of a bullet, and the effects of gravity as the bullet travels sideways and it gets far more complicated. If the rifle is level, and the scope is level, you take the sideways vector out of the equation, and now only have to deal with the up and down flight of the bullet.

 

[Mystic Precision]

GM, its all about your application and the requirements of your sport.

Ergonomics plays a major role in many disciplines and sometimes, the way the rifle fits the shooter may not be considered plumb BUT it does work.

Most target shooting is done on fixed distance targets and the vast majority only shoot at one distance. Having the sights not plumb with the 'rifle' may be completely acceptable in these applications.

For shooting at various distances especially when distances reach out, what you are suggesting IS correct. A small variation isn't going to make much difference but a major cant between bore and scope will throw off the scope adjustments.

There are many ways to shoot a rifle depending on the application (and body type) so keep an open mind and understand the other point of reference.

There is so much to learn from those shooters that do it differently.

Jerry

 

[AKD]

Big oll books being written up there.


Quick answer - no the scope does not half to be level to the rifle.

The scope just has to be level to the shooter.

 

[rnbra-shooter]

If you shoot with your sights level, then it all comes down to where the muzzle of the rifle is located with respect to the sighting axis of the scope. I.e. is the muzzle 1.5" directly below the scope's sight line? Or is it 2.2" below and 0.5" to the right? etc.

Before we get carried away with the esoterica ;-), remember that my initial comment was that a very small non-plumbness of the scope would be immaterial. I wanted to point out that all the precise alignment effort people make, is not in fact necessary and provides exactly zero accuracy benefit. A scope that is mounted 1.5" from the rifle's boreline but which is canted 2 degrees clockwise, will when the rifle is fired with the scope level, result in the muzzle being actually being located 1.49908" below and .052" to the left. If the scope has exactly the correct adjustments for a 1.5" sight height, then at 100 yards the bullet will strike less than one ten-thousandth of an inch low and .052" to the left. And at 600 yards, the bullet will also strike .052" to the left (note the same amount of offset at 600 yards as at 100 yards). This error is so small as to not be noticeable.

Now let's get on to the esoterica, just because it's more fun...

You can consider the adjustment put on a sight to consist of two components:
- the "trajectory compensation"
- plus the "offset compensation"

What I have called the "trajectory compensation" is the amount of windage/elevation needed to get the bullet onto the target if the muzzle of the rifle were co-located with the rifle sight. It consists of drop due to gravity and drift due to wind (and perhaps also spin drift and the other bits of ballistics esoterica).

Since the muzzle of the rifle is actually offset from the boreline, the "trajectory compensation" will deliver the bullet from its offset position at the muzzle, to a point on the target offset from the aim point by the exact same amount. So one needs to add an "offset compensation" to move the shots onto the aimpoint. In the example above that would be 1.5" low and .052" left, AT ALL DISTANCES. If you are shooting at 100 yards, you would have to add an additional 1.5 MOA to the elevation (because that's what it takes to move the bullet up by 1.5 inches at 100 yards). At 600 yards you would only have to add a quarter of a minute (because that's what it takes to move the bullet up 1.5 inches at 600 yards). At 1000 yards you would have to add 0.15 MOA, could be one 1/8 MOA click (if your scope has eighths), or zero quarter-MOA clicks, or one quarter-MOA click. In practice you'd never be able to tell this 0.15MOA error at 1000 yards. Note though at closer distances you need to make much bigger corrections - say at 25 yards, where you need to add 6 MOA of elevation in order to raise the bullet by 1.5 inches.

So interestingly enough, the *longer* the distance, the *less* noticeable the effect of an offset muzzle is (whether that is a simple 1.5" displacement below the line of sight, or something more complicated like say 1.5" down and 3" to the right, like can happen when an iron sights shooter with a bad eye has his sights on his rifle offset it order to line up with his other eye)

 

[jjohnwm]

Why do you suppose that so many long-range shooters, using scoped rifles or even BPCR's with tang sights, have levels mounted on their guns? It is because it matters! With any type of sight, optical or iron, the rifle barrel is pointed slightly upward (toward the line of sight), causing the bullet's trajectory to intersect the line of sight at two points. When the scope crosshairs are perfectly level, the barrel is directly beneath the sight and the bullet's trajectory lies entirely in that same plane, i.e. the plane defined by the bore and the sight. The bullet falls directly downward from the moment it leaves the barrel, and with respect to the line of sight it appears to rise above, and then fall below, intersecting at the sight-in distance the second time and then continuing to fall after that.

If your crosshairs are canted, your barrel is pointing off to the side of your line of sight. The bullet leaves the gun at that angle, but once it exits the muzzle it now begins to fall straight down. It is now moving both sideways and vertically with respect to the line of sight. Group size (accuracy) is unaffected, but your ability to place those groups on the POA at various distances by simply holding over or under, or dialing the reticle, is totally gone.

Your arguments above hold true only if the scope is parallel to, but offset to the side of, the barrel. A canted scope crosshair does more than that...it introduces many more variables than you are accounting for. Green Machine may be a "newbie"...but it seems that he understands this concept very well.

John

 

[rnbra-shooter]

John you write If your crosshairs are canted, your barrel is pointing off to the side of your line of sight, which is true and I agree with you - if you shoot with your *sights* canted, you will be introducing "windage artifacts". And the longer the distance (actually the more "up" elevation on your sight), the more vitally important it is to keep your *sights* as level as possible to avoid this problem. There is a famous Canadian target rifle book (Desmond Burke's Canadian Bisley Shooting written which has a very long, very technical chapter on what happens when you cant your rifle. A technically-inclined shooter can spend hours following through all of what he discusses, but there is a very simple summary that all shooters will find useful - DON'T CANT. Which I would like to clarify really means, "don't cant your sights".

What I am trying to point out is that if underneath your perfectly-level sights, your *rifle barrel* is slung a bit crooked it just doesn't matter (i.e. whether your bullet starts out exactly 1.5 inches below your line of sight, or if it starts out 1.4 inches below and 0.4" left of your muzzle (a 20 degree cant of your gun underneath your *level* scope).

Green Machine's status might say he is a "newbie" but that is because he only has a few posts; he has been here for a number of years and clearly knows his stuff. You he and I agree that one must keep the sights level when shooting especially at longer ranges. I am trying to make the point that as important as that is, it is unimportant for the action and barrel to be precisely slung directly underneath the scope.

 

[jjohnwm]

My apologies, Daniel...in reading and re-reading this thread and the other one, it appears that all three of us are trying to say essentially the same thing, and disagreeing more and more about how to say it!

Once you wrap your head around the idea, it is perfectly simple and easy to envision...but it isn't the easiest concept to verbalize. I worded my response very carefully, trying to draw a picture in words...and by the time I finished it and read it, I could barely understand it myself!

In any case, thanks for the debate. I can only imagine how much more interesting it would have been if we actually disagreed.

John

 

[injundon]

If Zeroed and shooting at only 1 distance it would make no difference. If you zero to 100 yards and are shooting say 1000 yards, With NO wind. and use your DOA or Mildots, or just click in the elevation difference. You'll have a big difference in accuracy.

if at 100 yards, your bore is 1/4" more left than your scope and zeroed for that. The bullets trajectory will have to shift 1/4" left@100yards, which would be 1/2" at 200 yards, 1" at 400. etc. Not drastic, but it's enough if shooting multiple ranges in a competition.

But as said, if you are zeroed at 1 range, and and only shoot at 1 range. it would make NO difference.

 

[green machine]

My experience comes mostly from shooting airgun field target. Targets are placed between 10 and 55 yards randomly. Smallest kill zone on a mechanical target is .25 inch, and the largest is 1.5 inch. So you have to hold over or dial your scope just like any other precision shooting discipline. Cant of a rifle can play a big factor at the farther distances, especially when you consider how bowed a pellet's trajectory is compared to a centerfire rifle. It seems the general consensus is at a fixed distance, not a big deal if your scope is slightly out of plumb, but at greater variations in distance, it can play a factor if you need to put a shot in an exact spot, the first time. Glad to be able to have a lively discussion, and hear everyones point of view.

 

[rnbra-shooter]

@injundon, if your bore is 1/4" left of your scope, then your 100 yard zero will include one quarter minute of right adjustment in order to bring the bullet onto your point of aim.

At 200 yards, it only takes 1/8 MOA to bring the bullet 1/4" to the right, onto your POA. So from your 100 yard windage zero you would have to take off 1/8 MOA.

At 300 yards, it only takes .083MOA to bring the bullet 1/4" to the right. So from your 100 yard windage zero you would have to take off 0.17MOA, or alternately from your 200 yard windage zero you would have to take off .04MOA (which is small enough to be a non-change).

At further distances, it takes ever fewer MOA to bring the bullet 1/4" to the right, onto your POA. Essentitally there is no practicably detectable change in your windage zero at any of these longer ranges. The biggest change you would have would be at the very longest ranges, where you would simply take off the entire one-quarter-MOA that was embedded in your scope's 100m windage zero.

At closer and closer distances, it will take more and more than 1/4 MOA in order to make that 1/4" correction. At 10m, it would take 2.5MOA in order to make that 1/4" move.

@green machine airgun shooting is the "worst" or perhaps I should say most sensitive to these effects, because the distances are so close. A quarter or half an inch of offset at 15m or 20m is many more MOA than the same amount of distance offset at centrefire rifle distance of 100m+.

 

[redshooter]

Who's on first...

 

[green machine]

I see your point. If your zero is at longer distances like 500 yards, then you would only be .25 one way at 0 yards, on target at 500, then .25 the opposite way at 1000. Not really significant at those distances. But if zeroed at 100 with the previous example, the change at 1000 would be 1.75(9 times your zero, past zero distance), possibly enough to throw away a match, I wouldn't take that chance.
Yes, airgun shooting makes all of the same things happen in a tenth of the distance. Any misalignment can have big effects when some shots can be well under 1 MOA.

 

[peacefrog]

Why not keep it simple? You can't, CANT. Period.

It does not take long to do, level the rifle, then level the scope. Yes it does/may not matter much at 100 yards, true, but it will matter at longer distances. So what if you are not a long distance shooter?

Why would you not set up your rifle to be as perfect as you can have it anyway?

Have a nice day.

 

[rnbra-shooter]

Why not keep it simple? You can't, CANT. Period.

Agreed - very good advice to give a shooter. Don't cant the sights when you shoot, keep them level.

It does not take long to do, level the rifle, then level the scope. Yes it does/may not matter much at 100 yards, true, but it will matter at longer distances. So what if you are not a long distance shooter?

Why would you not set up your rifle to be as perfect as you can have it anyway?

Have a nice day.

What I have been trying to point out, is that it does not matter if the *rifle* is level. There's no harm in levelling the rifle, but there's no benefit either; other than looking a bit silly a skewed scope is *not* doing one bit of damage to a rifle's accuracy, ESPECIALLY at long range (at extremely short distance, these offsets actually start to matter).

BTW I am a long distance shooter. I thought it would be useful for shooters to know not only what does matter, but also what doesn't matter. This can save time and effort when diagnosing problems, setting up rifles etc.

 

[ryandpahl]

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.

 

[dthunter]

Its actuall a little refreshing to see a group of guys(all who know thier stuff) debate on a forum!
Its frustrating to read or participate in a discussion where someone who is much less knowledgable keeps trying to derail a truthful respnse to a post.

I have wrestled with this subject for years. Simply put, all "I" do is try to make the rifle as vertical as I can, align the vertical crosshairs to a plumb bob line, then lastly make sure my scope level aggrees with the plumb line.
Havent had trouble since.
Never forget, have fun guys, and if the need arises, you can simply agree to dissagree.
Have fun and straight shoot'in!

 

[AKD]

Good post brother.


"I" as in me myself. I use a Horrus ASLI with a bubble level. Its epoxied solid right to my scope. Bubble level is level to the crosshairs. Very Important.


I also can say I shoot past 1200y. at that range you will do your dam best to keep the reticule level naturally,,,,, A buble level gives you the guarantee you want.

 

[injundon]

extreme example of barrel offset but theres the point.

Red is optical line through scope other line is bullet trajectory. Zeroed at 100yards...

oops goofed the drawing.. Figure the red line as trajectory silver line as optical.. I rushed it and Im tired

 

[AKD]

your photo sucks sorry
and this is why.

your scope rings in real life are inline with the bore. If not 100% close enough where a normal first time zero with the rifle and your good to go. Therefor this problem you pictured up here does not actually exist... If it does contact Savage or Remington. dont hide we know they built it anyway. They do have good service for manufacture flaws like that.

drawing kind of shows how a canted rail works..... if the gun was a lazer


A scope can be mounted even elce were from the barrel like on an artillery piece. Same thing still sticks with the level reticule. Vitally important for correct drop on large range targets.

 

[acm]

extreme example of barrel offset but theres the point.

Red is optical line through scope other line is bullet trajectory. Zeroed at 100yards...

oops goofed the drawing.. Figure the red line as trajectory silver line as optical.. I rushed it and Im tired

Makes sense to me, I was thinking about this with a 90 degree error too.

1. It seems to me that if your scope is not mounted level, but you hold your rifle level, your windage or elevation are not going to adjust just windage or elevation. Have fun with that.

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?