Correcting Scope Cant
Having fitted a new scope to my rifle, and successfully sighting in at 100 meters, the next step was to increase the range to see how well it would do at 200 and 300 meters. But before going to the longer ranges, I wanted to check if the scope was canted correctly.
Reading as much as I could on the subject, I found various tools that could be bought to level the scope in relation to the rifle.
All of them had a built-in level of some kind, and all put a level across the receiver, or across the scope turret. However none of them seem to first verify if the scope is aligned to the bore. Putting a level across the receiver assumes the top of the receiver is perpendicular to the vertical, and putting a level across the scope turret assumes the turret is perpendicular to the bore. Neither may be true. Or the reticle could be slightly out of alignment with the scope body.
On my rifle, the receiver is higher on one side than the other, so the spirit level method doesn't work.
I came across a web page on thefirearmblog.com - Levelling a scope reticle , that describes how to check for scope cant using a flashlight, so I've used that method and added an additional step in the process to align the mid-point of the reticle and the bore center to the vertical, before adjusting the scope cant.
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Here is a short how-to.
Suspend a plumb line on a smooth white wall or other surface
Put the rifle in a stand, butt to the line. Because the scope mounts are already fitted to the rifle, it's not necessary to find the vertical of the rifle itself, only to align the bore center and crosshair center to the plumb line.
If you align the bore center and crosshair center on the vertical, and the rifle itself is canted in the stand, then the scope mounts are probably not fitted correctly to the receiver.
Two lights are needed, one for the bore, and one for the scope. It helps if the lights can stand on their own, leaving your hands free to tighten the scope rings while the reticle is illuminated. A flashlight is handy to see the screws when tightening the rings in the low light necessary to see the projection on the wall.
The bore light needs to be brighter than the light through the scope, or you won't see it.
You'll need to do this in a darkened room.
First shine the bore light through the bore, and center it on the plumb line by moving the rifle stand.
Then switch on the light through the scope.
Lastly, with both lights on, align the center of the bore and the center of the crosshair on the line, which will ensure the center of the bore and the center of the crosshair is in the same vertical plane. Now you can set the cant. This scope was out of vertical, I estimate around 3 or 4 degrees.
Keep the flash-lights on while tightening the rings, because if the screws are not tightened evenly the cant will shift, and keeping the light on shows any movement of the reticle while tightening. The rifle needs to be firmly in the stand so that it doesn't move when tightening the screws on the rings.
Lights that can sit in place are very handy because it's not possible to hold two lights in two places and tighten rings at the same time.
The brighter the lights, the further from the wall you can have the rifle, and the more accurate this method will be.