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.
My method improves the single flashlight method - Levelling a scope reticle , that describes how to check for scope cant using a flashlight and a plumbline.
I use two flashlights and no plumbline.
With one flashlight, all you have is a seemingly vertical reticle, with no reference as to where your bore lies relative to that. Shoulder the rifle and you will probably see that the reticle is not straight.
Levelling the receiver with a spirit level just means you have a level receiver, it does not mean your bore is aligned to the scope.
Levelling the scope with a spirit level means you have a level scope, it doesn't show where the bore is in relation.
This method proves the bore is not offset from the crosshair vertical. In other words, it totally eliminates induced windage due to a non-vertical reticle.
Align the vertical line of the reticle to the bore center. Done.
This method makes sure that the vertical of the reticle is exactly aligned to the center of the bore.