Saw it here on another thread, I take no credit: Mount rings in opposite directions. screws on opposite sides of the rail with the two rings touching to check them for centering on a rail. Cheap mounts may not match up and require you to adjust farther to the edge of the optic center than good ones may.
I can pretty much guarantee that MOST mounts will not line up, if you fit them with screws on alternate sides.... if for no other reason than there is little standardization on dovetail widths on airguns.... As Jason said, a slight offset is not an issue, as long as the vertical crosshair bisects the boreline....Bob
Additionally, if the vertical crosshair intersects the bore with the scope optically centered.... and you hold the crosshairs level when shooting.... the only time you will have to dial in windage is if the dovetails are not parallel to the bore.... or if the rings are off center (like might happen if you reverse one ring).... The most common error made in mounting scopes is trying to correct offcenter mounting by cranking in windage.... instead of rotating the scope in the rings (while the scope is still optically centered) until the crosshair intersects the bore.... and then canting the rifle if necessary to get the crosshairs level when shooting....I had several scopes where the windage was cranked over a long ways.... every one of them returned almost to center by first optically centering the scope, and then rotating it in the rings until the vertical crosshair intersected the bore.... Only slight windage adjustment was then necessary to fine tune the zero....Bob
I would optically center the scope before aligning the crosshairs with the bore.... but you don't need to be anal about it.... Counting the clicks and setting the scope in the middle of its travel is good enough.... Then once you use the mirror and align the crosshair with the bore, you won't have to crank in a bunch of windage, and will remain close enough to the optical center of the scope....Bob
This guy set up two identical scopes with quick release on a 6.5 Creedmoor. One had the scope reticle aligned to the flat on the receiver. The other had the vertical cross-hair aligned to a plumb line, despite the rifle being slightly canted to match the shooters comfortable hold: youtube.com/watch?v=eCoHG23TQcYThe results may surprise you...