I have the Wheeler scope level kit with 2 levels. Place the first one with the scope removed on your pic rail and adjust in the vice until level then the second one goes on the barrel and adjusted to match the first one so you can then remove the first one and put your scope on. You then place the first one on your turret as you described with the cap off and adjust the scope until it matches the level on the barrel that is now your reference. I've been using this system for many years now and am not afraid to swap scopes around at all. Works awesome!.
Yes, but it depends. Ah, life always has a caveat. It will be level to the top surface of the picatinny rail. Remember to push scope forward....and downward.... securely against rail while tightening cross bolt. Only exception if the picatinny rails between rifles are machined incorrectly.....minimal probability...or the rifle mounting surfaces are not uniformly square/level....possible but minimal. Picatinny rail bedding might cause variation....solid mount, but variation between rifles is possible. The following proven device does the same function. Badger Ordnance, Kansas City, Kansas, makes the Badger Dead Level scope mounting rail consisting of a picatinny rail mounted on an aluminum base with a bubble level and leveling feet P/N BO-0200 for $134.95. Level the device on a solid surface visa the bubble level, then mount your scope to the pictanny rail as though it were your rifle, leveling reticle to picatinny rail via any number of methods......flashlight through ocular lens onto wall with plumb bob level string, or other preferred method. (These methods assume the reticle is plumb to the scope housing mounting base. Always question that assumption until confirmed via tall target tracking test.) Then, transfer scope in the rings to your rifle knowing it is dead level. I do this with all my scopes, followed always by tall target tracking confirmation, if to be used at ELR......assume competency but always confirm. Minimally critical for hunting kill zone and within 500yds. Only easier option is single scope mounted to a change barrel rifle.
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Wow very cool but dang that is expensive lol.