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Mounting and squaring the scope

This is a discussion on Mounting and squaring the scope within the Optics forums, part of the Gun Forum category; Originally Posted by 2336USMC Well, there are many ways to skin the cat so to speak. We are simply saying the same thing viewed from ...


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Old March 12th, 2017, 06:12 PM   #31
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Originally Posted by 2336USMC View Post
Well, there are many ways to skin the cat so to speak.
We are simply saying the same thing viewed from different perspectives.

I am also a lifetime iron sight shooter. As you say, using irons, the rifle must be vertical. And, through practice, you have probably grown accustomed to mounting the rifle in the shoulder pocket vertically.

When I mount a rifle there is an amount of cant. Most shooters have some, it's just the way the buttplate fits into the shoulder. If I'm shooting irons there is no other choice than to adjust to remove the cant, check level, sight, press and fire.

With my adjusted scope I just put the rifle to my shoulder. Cant never enters my mind, it is meaningless, only that the rifle is perfect in my shoulder, comfortable and the reticle is already level. So check level, sight, press and fire. Just as you do.

It is because I don't shoot on the same range with the same bag, the same bench, etc that I do this. In real world shooting the rifle will come to the shoulder in a specific, repeatable orientation. Yours is likely vertical. Mine just happens to have about a 2* cant. So I adjust the scope so it's level with my natural 2* cant. My reticle is not canted, my rifle is. But looking through the scope my sight picture looks exactly like yours. In real world shooting as long as the reticle is level accuracy is not affected.

Some people say tomato, some people say french fries .. or something like that.

Thank you,
Mr.Smith

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Old March 12th, 2017, 06:23 PM   #32
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Originally Posted by Fishjager View Post
This is a great reply!!! Especially discombobulated! What does that mean anyway? I happen to agree with you on the scope that is canted. That is why I started this thread.
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Old March 12th, 2017, 07:46 PM   #33
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Rich, As you mentioned, the rifle must be perfectly level. I use a level that is known to be true and place it on the flat part of the receiver just behind the rear sight to level the rifle.

Rich
I finished re-checking one of my scopes that gave me trouble. The rifle was not shooting accurately last summer (yeah could have been me). But I’m guessing the scope was slightly off alignment from the way I did the plum bob method. Let me explain the mistake I made.

Being an old math teacher I will re-state the problem mathematically with geometry. Imagine the barrel and scope in a Cartesian coordinate system in three-dimensional space. First we draw a line down the center of the rifle bore as our center axis - the X1 axis. Then we draw a line down the center of the mounted scope as our second X2 axis.

Defining the plum bob method

In a perfect installation for the plum bob method the X1 rifle bore axis is parallel to the X2 scope axis and the plumb bob aligns them both on the Z1 vertical plane (90 degrees vertical) . This is the objective.

The first problem that can occur is the X1 rifle bore axis is parallel to the X2 scope axis but they are no longer in the Z1 plane (90 degrees vertical). This is the Cant error we are talking about. So a Cant error is the result of not holding the rifle bore axis and the scope axis in a vertical plane.

The second problem that can occur is the X1 rifle bore axis is NOT parallel to the X2 scope axis when we try to plum bob.

So if we use a level that is known to be true and place it on the flat part of the receiver just behind the rear sight to level the rifle, it will fix the first problem 100% of the time and eliminate cant! However the level will not fix the second problem. The method of hanging a weighted string some distance down range, and then for example bore sighting onto that string (or using a bore sighted laser) and then lining up the crosshairs on the string still only accomplishes a "one point in space" accuracy and assumes the rifle bore axis and scope axis are parallel.

I realized in this discussion that my scope mount rings on my rifle were probably screwed up when I installed them. I don’t know. It is not a cant error. In my case the X1 rifle bore axis is probably NOT parallel to the X2 scope axis for what ever reason. I remember having trouble installing those scope mount rings and the scope did not seem snug the way it usually does.

Rich


Last edited by rabbitone; March 12th, 2017 at 08:05 PM.
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Old March 13th, 2017, 12:01 PM   #34
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I set my rifle rest on a level table, plumb the rifle in the rest by holding a square on the table and against the butt pad centerline, sight on a vertical door edge, and rotate the scope.

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Old March 13th, 2017, 06:01 PM   #35
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Originally Posted by rabbitone View Post
I finished re-checking one of my scopes that gave me trouble. The rifle was not shooting accurately last summer (yeah could have been me). But Iím guessing the scope was slightly off alignment from the way I did the plum bob method. Let me explain the mistake I made.

Being an old math teacher I will re-state the problem mathematically with geometry. Imagine the barrel and scope in a Cartesian coordinate system in three-dimensional space. First we draw a line down the center of the rifle bore as our center axis - the X1 axis. Then we draw a line down the center of the mounted scope as our second X2 axis.

Defining the plum bob method

In a perfect installation for the plum bob method the X1 rifle bore axis is parallel to the X2 scope axis and the plumb bob aligns them both on the Z1 vertical plane (90 degrees vertical) . This is the objective.

The first problem that can occur is the X1 rifle bore axis is parallel to the X2 scope axis but they are no longer in the Z1 plane (90 degrees vertical). This is the Cant error we are talking about. So a Cant error is the result of not holding the rifle bore axis and the scope axis in a vertical plane.

The second problem that can occur is the X1 rifle bore axis is NOT parallel to the X2 scope axis when we try to plum bob.

So if we use a level that is known to be true and place it on the flat part of the receiver just behind the rear sight to level the rifle, it will fix the first problem 100% of the time and eliminate cant! However the level will not fix the second problem. The method of hanging a weighted string some distance down range, and then for example bore sighting onto that string (or using a bore sighted laser) and then lining up the crosshairs on the string still only accomplishes a "one point in space" accuracy and assumes the rifle bore axis and scope axis are parallel.

I realized in this discussion that my scope mount rings on my rifle were probably screwed up when I installed them. I donít know. It is not a cant error. In my case the X1 rifle bore axis is probably NOT parallel to the X2 scope axis for what ever reason. I remember having trouble installing those scope mount rings and the scope did not seem snug the way it usually does.

Rich
Hello Rich,

I think that you may be over thinking the solution of a really simple problem, just my opinion. As the saying goes, " There's more than one way to skin a cat" and if it works for you, go for it.

Rich

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