Actually you can cant your rifle with no ill effects as long as you are holding the reticle level. An extreme example would be David Tubbs rifle
After going through a scope rotation and canting problem, I now use and EXD Device EXD ENGINEERING VERTICAL RETICLE INSTRUMENT at Brownells
to align the scope with the bore. If you set your rifle up in a vise and use the EXD that will insure that the rifle is uncanted. Then you rotate your scope to level the crosshairs on some distant object, I use a 4' level on a fence 30 yards away. When you get the crosshairs level and the EXD device level and lock things down then you have a good start.
But you have to transfer that level to the field. Like overbore, I use an anti-cant device, usually one of these
but I also have one of these
which are the best since you can aim and level without losing cheek weld.
After all, 6 degrees of cant sounds like a lot, but it is only 1 minute on the clock face.