Many hunters try to eke out the last vestiges of accuracy for their favorite hunting rifles by switching bullets, playing with optimal seating length and other standard techniques. But what if I told you that you that are potentially throwing away .2 to 1.2 MOA because your scope is not aligned perfectly?
When your scope is not is truly vertical, it will cause your bullet to impact to the right or left, depending on the direction of the cant. A five degree cant will result in an error of 3.7 inches at 300 yards. That may not sound like much, but if you are trying to hit a ten inch vital area, it means you must shoot less than 1 MOA or you risk missing—and that is before any wind deflection error. Suppose you cant to the right 5 degrees; your group will impact 3.7 inches right and you will have only 1.3 inches of vital area before you risk missing to the right, which means you must shoot 2.6 inch groups at 300 yards, or less than 1 MOA. Without any cant, you can shoot 3 MOA and still connect.
There are lots of fancy kits sold that allow you to mount a scope so that it is level, but there is a simple tool that I find indispensable: the Segway Reticle Leveler. But instead of using the horizontal line wings to align the horizontal crosshair by looking at it, I use it to ensure my rifle is level.
You will need an area about 20 to 30 yards with a vertical line; I use my pool fence, which has bars that I have checked with a carpenter’s level to ensure they are perfectly vertical. You can use a rope on a plumb bob or set up a target with a piece of tape which you have adjusted with a carpenter’s level to be perfectly vertical. After ensuring the rifle is unloaded, place your rifle in a front and rear rest. If possible, find a flat spot on the action; if you use a Picatinny rail you will find the Segway alignment bar fits in the rail notches. Attach the other plastic wing and then loop the elastic band under the rifle and secure it in the hooks. Rotate the rifle so that the level on the alignment bar is level. With the ring screws loose enough to rotate the scope in the rings, you are ready to adjust the scope.
Looking through the scope, align the vertical crosshair with your plumb line. Check the Segway bubble level and rotate the rifle so that it is level. Now rotate the scope so the vertical crosshair is aligned with the plumb line. Finally, tighten the rings, checking frequently to ensure the vertical crosshair is still aligned with the plumb line and the Segway bubble is level. Once everything is done, I attach a ScopeLevel to my scope and rotate it so that it is level when my vertical crosshair is aligned with the plumb line. You might not think this is necessary, but in the field the ground is rarely flat, and without an anti-cant device, you will often cant your rifle, which defeats the whole purpose of insuring your reticle is level.
Do I do this for every rifle? Of course not. I hunt deer every year in northern Minnesota and never bother—but then, nearly all of my deer have come under 50 yards, the longest shot being 150 yards.