I use that but differently than recommended. I place the bar in a rail cut-out, and then with the rifle on a bipod or other rest, make sure the rifle is canted to be level. Then I align my vertical crosshair with something I know to be level. When I am in Phoenix, I use a 20 story building far off in the distance. I know the sides are plumb because when I bracket the top of building (which is flat) with my horizontal wire, the vertical fits perfectly along side the vertical side of the building. In the past I used my pool fence as a plumb line (verified with a level and square) but I prefer the building alignment now.
Once I have the scope rotated correctly, I place a level on the top turret as a second verification, then carefully tighten the screws. When everything is tight, I verify the level on the rail is level, my building bracket is square, and the level on the turret is level. I often have to repeat because the scope often slips just a bit while tightening.
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're potentially throwing away .2 to 1.2 MOA because your scope is not aligned perfectly?
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