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Scope leveler device: canting a rifle will always degrade accuracy to some extent but there are positive measures that can be taken to alleviate this on our way to reliable accuracy. Here's how to make, install, and test a scope leveler.

As a measure in the process of eliminating--or at least reducing--the effects of accuracy-robbing scope canting, we can install a scope leveling device designed for the purpose. These levelers are for sale and range widely in price, or we can conveniently make them from readily-available materials. This will be the approach covered in this treatise.

As a rifleman and gunsmith, it behooved me to determine precisely how rifle canting actually affected bullet impact on target. Some years ago, and more recently, I conducted definitive tests to reveal the effects of rifle sight canting. As a scoped rifle is shot, the sight reticle (crosshairs) should be perpendicular to the aim point on target, or as uniform as possible from shot to shot. Under normal shooting conditions a shooter can arrive fairly close to maintaining a vertical and horizontal scope reticle without canting error, but it seldom occurs. Errors here are more critical while target shooting or shooting game at long range. The insidious effects of scope rotation can creep in as the shooter aims and shoots the rifle from shot-to-shot.



Depending largely on the height of the scope above bore axial center and the ammunition used, as little as a few degrees of cant can cause the bullets to impact from the intended aim point. Where the rifle is canted right, the bullet will hit right and low of aim. A like deviation occurs where rotation is left.



While not dwelling on a lot of geometric technicality, I'll elaborate on the harmful effects of canting a riflescope as we shoot and show how to make proper corrections.

Canting error on target occurs when the barrel axis is rotated out of the vertical plane. As a scope is mounted well above the bore axis, the bullet must cross the line of sight at about 25 yards and then again cross the line of sight at the point where the rifle is sighted in. This sets the stage for right or left impact errors depending on how much the barrel is canted out of the vertical plane. Cant rotation causes the bullet to impact in the direction of rotation with at least some drop as an effect of trajectory. In all cases, canting a rifle will be harmful to precision and accuracy, but there are corrections that can be made to alleviate this.

Making A Scope Leveler Device

The pictures will serve as a guide in making a scope leveling instrument. As a part to hold the level used in making the leveling device, I used a common Redfield Jr. high-height ring. A front or rear ring will suffice. I also used a pair of aluminum rings of another style with a sufficiently high base for the same purpose. Either one-inch or 30mm scope rings can be used.

A 3/8-inch hole was drilled and reamed at center on the underside of the base to about 1/2-inch depth. Four small set screws were drilled and tapped around the bottom perimeter of the base to hold the inch-long 3/8" diameter spirit level. With level inserted to desired depth, the four set screws are lightly tightened. The level is essentially self-aligning in the base hole.


Attaching To The Rifle

When installing a leveler, always begin with the rifle held precisely perpendicular in sand bag rests or other method of holding. There must be no cant or rotation right or left. This requires some attention to detail, which can be deceptive. The rifle must be precisely aligned with a level, not just by eye. A perpendicular line on a paper attached to the butt plate will work fine after checking with a small machinist's level.



The next critical step is to align the scope reticle precisely perpendicular with the squared rifle. If this, isn't accomplished, the scope reticle will be at an angle with the rifle. This can be checked out by aligning the scope reticle with a known object that is level or perpendicular. The rifle must therefore be kept in a perpendicular position as the scope is leveled.

With the rifle maintained in true vertical position, the leveling device is attached with the level bubble at true level. The modified rings used as the leveling device can be clamped to the scope just ahead of the rear ring on either side of the scope. While it is easier to see on the left side of the rifle, it is less likely to be damaged while carrying the rifle if attached to the right side. Double check the perpendicular position of the rifle and scope reticle as necessary from time to time.

So now we have the rifle, the scope reticle, and scope leveler device all calibrated, leveled, and ready to put to the test. I made up a special target using an angle rule to indicate the position of the scope reticle in degrees of perpendicular alignment. This test target makes it possible to aim the rifle to the exact degree off level shot-to-shot. The degree of shot displacement or error on target will depend on scope height above the bore line, bullet trajectory, and distance. Bullet impact will vary. This leaves nothing to guesswork.


While adding a leveling device to a rifle may not improve its inherent accuracy, it will alert us to the effects of accuracy-robbing cant. If we can nullify this untoward problem, groups are sure to improve.

by Norman E. Johnson
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Title Annotation:WORKBENCH
Author:Johnson, Norman E.
Publication:American Gunsmith
Date:Aug 1, 2017
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