He’s saying it’s better to index off the bottom of the turret housing bc the reticle is true to the bottom of the housing. Guys put levels on the tops of turrets and often they are not actually plumb. The Arisaka tool is the easiest way to get your scope level if you have full pic rail.
Can you tell me what the difference is for the long action magnums and the ultra mag is? What’s best for a 7 prc? I’ve seen some listings saying the RUM is the same as the PRC cut.