Well actually I don't much care for the ergonomics of a scope-mounted level. It's just that they always work because they can be rotated to fine tune for a proper level indication.
Please bear in mind most scope mounting strategies that involve the use of levels or wedges (e.g. Arisaka) are making a variety of assumptions about the perfectness of critical features of the gun, scope, and mounts. Granted, frequently these items are close enough that you’ll get a better result than by just eyeballing it, but it’s frustrating to see jigs that will leave you with an improperly aligned scope if something isn’t perfect. For example it’s not uncommon for the reticle to be rotated a couple of degrees relative to the scope body or turret caps, in which case having installed the scope with the help of wedges will result in a canted reticle.
And that's just one of at least half a dozen issues that can yield an incorrectly installed scope. What matters is that the reticle is aligned to the bore, and the good news is it can be done with no special tools. All you need is a mirror. Set it up at a distance of, say, 5 yards and set your scope's AO to 10 yards. Look through the scope at your reflection in the mirror. Twist the scope in the mounts until the vertical bar of the reticle simultaneously bisects both the muzzle and objective bell. Then lock it down. At this point you have eliminated scope cant beyond a shadow of a doubt.
With the scope now properly oriented, view a known good plumb line (e.g. hanging string) through the scope and orient the rifle so it precisely aligns to it. If the rail-mounted level doesn't show level, it needs to be shimmed until it does. If using a scope-mounted level, it can simply be rotated to show level.
From this point forward, you can use the level and be assured the trajectory will lie precisely in line with the reticle.
