I am new to the forum and have not posted much. I was very bad as far as canting a rifle because I used to shoulder where it felt good and rotate the reticle accordingly. Only after getting into long range hunting/shooting did I learn of the importance of having the reticle truly plumb to the bore. In fact like many on here I have become anal about that endeavor to the point I have purchased and used just about every kind of leveling device available. It is from that experience I submit this post hoping to share my findings and help others with regards to such purchases.
I have the Wheeler level/level system, the Brownell tool, and the Segway. I will limit this to those tools as they are the most widely recommended and used. What I have found is none of these tools can stand alone as "THE" tool. I have used various combinations of these and some of the other "levels" I have acquired over time. The one tool I have used consistently is the barrel level in the wheeler system to transfere my rifle leveling to the barrel. I have tried all of the other systems and have not found any of them to be full proof depending upon the action/mounts. The Wheeler rail level is pretty good but I have found on some application you must be very careful in how you place it in on the rails as it can easily give false readings and it simply will not work on some actions.
I have placed a level on the action bars, a pictinny rail and the bottom of both rings and gotten a variety of readings all at the same time. I have seen pictinny rails "read" different from front to back and the same with rings. By using several different points of reference on a particular rifle I come to a consenus of what truly level is. One of the most reliable "tools" I have come up with is a properly sized piece of steel bar stock slid in place of the bolt on the action rails. If sized properely it works the best for me. On a number of occassions when using this method and placing levels on rails and bases some of them will "confirm" the reading but there is usually one that is a bit off. After getting a read on the action I transfere that to the Wheeler barrel level so then I can get them out of the way to facilitate mounting the scope. I then proceed to a wooden vise outside to hold and level the gun and use a DOTTED level line I have painted on a building to match up the reticle. The dotted line really aids in getting a better alignment with the reticle. I do this while the rail level and/or my bar stock is in place and "confirming" the gun is level and the barrel level is true.
So my answer is use a combination of the upper end tools as I have gotten the reticle aligned as described while the barrel level and action level all agreed and a level on the turrent did not. I think the final test is to shoot it "up the line". This is what I have found, using a combination of the tools as a checks and balance. I have found the Wheeler system and the simple piece of bar stock to be the most usefull. I have found some satisfaction with the brownell tool although I would not spend the money for one again. I have not gotten the segway to work with any satisfaction to date.
I apologize for the long post and hope some find it useful. I know at first I was surprised at how far off rails and rings where but have now learned that is the norm and leveling off the action internally vs. externally is the way to go. The exception is custom rifles
/actions which are far more true to the bore.