scope mounting with laser level

[scott]

I read about hanging a weighted line on the wall to line an optic but wasn't sure how to easily level the gun out. but this seemed to work awesome.. maybe it's been done before.

laser level. vertical and horizontal lines on at same time. horizontal line used to level the gun in stand. then vertical line on wall to line scope up in rings. (line is straight, camera is crooked...)

 

[SavageLapua]

It looks like you have a one piece base for your mount? What I usually do is use a deck of cards or a set of feeler gauges between the base on the rifle and the flat on the bottom of the scope. Takes all of the guess work out. Just make sure as you torque in stages that the scope is still making equal contact on the cards/feeler gauge.

Once I have the scope mounted and have the anti-cant level mounted, I do a "tall target test" at the range. This confirms that the scope is mounted plumb to the action and also confirms the elevation adjustment is calibrated correctly (sometimes, even on high quality optics, there can be a small percentage of error on this adjustment). Below is an article by Brian Litz on the "how and why" of the tall target test.

http://bulletin.accurateshooter.com/2015/11/calibrate-your-clicks-with-tall-target-test/

SL

 

[Maple57]

Altogether too much effort is put into leveling scopes.

A scope can be off 10 degrees to the rifle and as long as the scope is level when fired, will have no meaningful difference in point of impact.

The scope needs to be level when you shoot.

The scope does not need to be level to the rifle.

 

[grauhanen]

The laser level is a good idea that is simple to use.

The need for the scope to bte level (plumb) with the rifle is less important if all the shooting is at the same distance. When everything is properly lined up, shots hit without the POI moving to the left or right as distance changes. This is shown in the top left diagram below. When either or both the scope or rifle are canted (out of plumb or alignment with one another) the point of impact will vary according to distance.

 

[Ghys_T3LSS]

Altogether too much effort is put into leveling scopes.

A scope can be off 10 degrees to the rifle and as long as the scope is level when fired, will have no meaningful difference in point of impact.

The scope needs to be level when you shoot.

The scope does not need to be level to the rifle.

If you always shoot at the same distance you are right.

If you increase distance, you will get an increasing right or left shift. The further you shoot, the greater the error.

Some images/drawings explains this well.

 

[Winz]

As mentioned above, a lot of attention is paid towards scope mounting which may or may not be very critical. The point would be in insuring consistency and repeatability not only in shooting at given distances but also for ease of adjustments (turrets) and/or use of reticle. This is why a scope should be level to the eye when shooting. If the reticle is canted, then calculations or adjustments are much more difficult since you are working on a different plane.

However, if one is always consistent with cant, this may also not be a huge problem either. This is common in the example of target shooters (ie with diopter sights at specific distances). Although the sights are adjustable for elevation and windage, it is not uncommon for rifles to be canted slightly depending on the shooter's practiced position. Typically, these types of shooters fit the rifle to their bodies and practice their positions heavily but nevertheless some still don't hold the rifle straight.

Use of laser level: This is a good idea and essentially the same as the traditional plumb line for scope alignment. In regards to leveling reference of the scope and rifle itself, it is probably best to use the rail base as your reference rather than the stock or even the receiver interface. A stock or receiver may not be perfectly square/parallel to the rail. The rail itself should be parallel to the x-axis of your reticle.

 

[maynard]

However, if one is always consistent with cant, this may also not be a huge problem either. This is common in the example of target shooters (ie with diopter sights at specific distances). Although the sights are adjustable for elevation and windage, it is not uncommon for rifles to be canted slightly depending on the shooter's practiced position. Typically, these types of shooters fit the rifle to their bodies and practice their positions heavily but nevertheless some still don't hold the rifle straight.
.

Somewhat true. Many smallbore shooters and 3P shooters do get away shooting with a can't and 50m. Standing 10m air rifle, just about everyone cant's. However I think most long range iron sight shooters or at least 95% that I know use a level in or on the front sight.

 

[Winz]

Somewhat true. Many smallbore shooters and 3P shooters do get away shooting with a can't and 50m. Standing 10m air rifle, just about everyone cant's. However I think most long range iron sight shooters or at least 95% that I know use a level in or on the front sight.

Yes, exactly right. At short, fixed distances it's less important. And absolutely true, at longer distances (like those shooting large bore, 1000m ironsight) are going use a spirit level on the rifle.

 

[Maple57]

While the geometry depicted seems correct, it actually is not in all cases. It actually simply illustrates the bias held by its creator.

The 2 far right upper examples are the only ones that are 'almost' correct as they attempt to illustrate what happens when the rifle is fired when the scope is not level and that is correct.

The top row left 3 assumes the rifle is perfectly zeroed in all cases and the shooter is aiming at the aiming point. The bottom row attempts to track the bullet past the aiming point which is not relevant.

The left to right misalignment error between the scope and rifle is actually parallel and not angular as suggested.

The error does not magnify over distance. If there is an error of 1/10th of an inch at 100 yards, the error will be 1/10th of an inch at 1000 yards, which is well inside the click value of a scope.

If the error did magnify as per the image, it would actually be beneficial as it would help offset the effects of spin drift.

Spin drift will walk a bullet to the side and require leftage on the turret that increases with distance.

If I was to consider the relationship between the scope and rifle I would contemplate tilting the scope to compensate for the effect of spin drift, particularily if I didn't want to calculate for it on the fly.

This effect can be created by adjusting the level out of alignment with the reticle to create about a 1 MOA tilt at 30 MOA on the reticle, but the actual amount would depend on the actual ballistics of the load.

As a finer point... a deliberate scope rotational offset could also be beneficial to neutralize a delta between the POI and the click value of the scope, in the likely case that the POI does not happen to be coincidental with a clickable point.

I think where guys get confused is they mistakenly confuse the need for the scope being level to the rifle when mounted with the need for the scope to be level with the world when fired.

The laser level is a good idea that is simple to use.

The need for the scope to bte level (plumb) with the rifle is less important if all the shooting is at the same distance. When everything is properly lined up, shots hit without the POI moving to the left or right as distance changes. This is shown in the top left diagram below. When either or both the scope or rifle are canted (out of plumb or alignment with one another) the point of impact will vary according to distance.

 

[Alpheus]

The error does not magnify over distance. If there is an error of 1/10th of an inch at 100 yards, the error will be 1/10th of an inch at 1000 yards, which is well inside the click value of a scope.

That is incorrect.

 

[Maple57]

That is incorrect.

Read the last line in my previous post twice!!!

Repeat as needed.

 

[Alpheus]

Read the last line in my previous post twice!!!

Repeat as needed.

Have you ever actually tested your claim? Because I went to the range this afternoon and did exactly that.

Let us review your statements:

A scope can be off 10 degrees to the rifle and as long as the scope is level when fired, will have no meaningful difference in point of impact.

and

The error does not magnify over distance. If there is an error of 1/10th of an inch at 100 yards, the error will be 1/10th of an inch at 1000 yards, which is well inside the click value of a scope

Rifle:

Scope is canted approx 15 degrees, the max allowed by the Atlas bipod without adjusting the legs.

Scope was leveled with bubble level by using a plumb line. Scope is Kahles K624i in MDT rings with 20moa base. A tall target test was also performed, results were excellent.
Weather was good, -4deg and a mainly headwind of 5-8mph
Ammo is .223rem loaded with 77gr Sierra TMK at about 2845fps.

Groups:
I shot at 49yards, 102yards, 216yds and 299yds, although my LRF is not super precise and thus ranges are +/-
Groups were shot with the scope level, paper target was leveled each time using a plumb line. I found the canted position of the butt and cheekpiece quite comfortable.

Groups were shot without re-zeroing after canting scope, although this would not have made a difference as the windage shift was not constant. Interestingly, the shift's actual size increased while the angular size decreased.

Measurements:
Range Windage Elevation
49 2.496” -0.604”
102 3.904” 0
216 4.6875” 4.875”
299 6.1875” 13.1875”


Range Windage Elevation
49 1.416mils -0.343mils
102 1.064mils 0mils
216 0.603mils -0.627mils
299 0.575mils -1.226mils


I would be very interested if you or someone else could replicate this test, perhaps with a different cartridge at similar distances.

 

[Why not?]

While the geometry depicted seems correct, it actually is not in all cases. ......

I think where guys get confused is they mistakenly confuse the need for the scope being level to the rifle when mounted with the need for the scope to be level with the world when fired.

Yes, and not difficult to prove by intentionally mounting scope with a severe cant, sighting in at 100, and shooting at longer distance with the scope level.

BTDT. As well, several guys here shoot with their rifles deliberately canted for better hold, all the way out to 600 meters without adjusting windage at any distance.
Ted

 

[Maple57]

Alpheus ,

I'm not sure what you are trying to illustrate and if it is counter to my post.

Did you shoot the rifle while the scope was canted and not level the SCOPE when firing?

Or did you shoot the rifle while the scope was severely canted but positioned directly above the bore as in the picture?

I have an idea that I hope will help...

How about I use letter O as a visual aid?

............O................ This is your scope and it is level

................O .......... This is your bore while the scope is level

................O .......... This is the impact while the scope is zeroed and level when fired at zeroing distance

............O..O........... The Left O is where you aim, the right O is where the bullet hits when zeroed at zeroing distance.

If you forget this error is even there and go about making scope changes for distance, the bullet impact will always be just 2 dots to the right.

You can fire the rifle to infinity in outer space and the impact would be offset by this exact same amount.

Here's another example...

............O................ This is your scope and it is level

................O .......... This is your bore while the scope is level

............O .......... This is the impact while the scope is zeroed and level when fired at zeroing distance (This induces an angular offset of 2 dots)

........O..O........... At twice the zeroing distance the bullet will now hit to the left of the point of aim by 2 dots.

If you are really concerned about this point, I would suggest that you redirect your energy toward the click value error that is greater than the minimal scope cant error one would have without using lasers to level the scope.

Most MOA scopes click in .25 MOA clicks and Mils are more like .36 MOA per click.

So one way or the other, you can only zero the scope to within 1/8th MOA to .18 MOA and a little scope cant might just minimize that.

 

[1-trident-1]

you just described an offset scope, not a canted rifle.

 

[Maple57]

Correct... I was speaking to the relationship between the scope and rifle when the scope is mounted.

Canting a rifle and scope has a different effect depending on how much elevation is applied to the rifle.

The higher you crank the scope, the greater the need for precise leveling of the scope.

If, for example the scope and bore were parallel, you could spin the rifle any way you want and the impact error would never be greater than the scope height above the bore. (Good trick for shooting overhead flying birds with a 22LR BTW.)

Once you throw 30 MOA of elevation on it, now you have a 30 MOA circle out at the target distance.

Angle the scope and rifle to 10 O'clock and you will get an impact that is along that 30 MOA radius out low and to the left.

 

[Alpheus]

you just described an offset scope, not a canted rifle.

No, the scope is rotated within the rings. Offset would be a translation left or right.

This is how the it was set up during the groups:

The point is the bore and line of sight of the scope are not parallel, like 95% of long range shooters I am using a angled scope base.

Notice how the two points of aim for the three groups are aligned vertically? If your dots diagram was correct, then the groups should all line up "two dots" to the left of the line running down from the 216yd PoA. If you zoom out to include the 299yds group, it too is not vertically aligned "two dots" over.

 

[Alpheus]

If I didn't have a tilted scope base, then this would be the case:

And each group would impact 0.517" to the right of the point of aim, at every distance (assuming perfect grouping).

But because the scope line of sight and the bore line of sight are not parallel, the 20moa changes from only effecting the vertical to having a horizontal component as well.

 

[Alpheus]

If I had dialed the elevation, the opp value would have decreased as the bore comes closer into line with the scope. And since the 15deg is constant, the adj value would've decreased as well, hence the mil values of the shift are decreasing.

 

[1-trident-1]

you are correct, I was referring to another poster. thanks for the time and effort to actually show the effects of cant on target and distance. you are an asset to this site.