Demonstrating 'parallax' effect in a Simmons 3-9x40 at 50 yards. The opening in the copper plate is ~1.5", note how far the crosshairs wander just by moving the camera (or your eyeball) around. The rifle was completely untouched in this demonstration.

Since this scope provides no adjustment for parallax, I'm wondering if backing off the relief a bit and centering the black 'halo' in the reticle is a reasonable means of properly aligning the line of sight with the optical axis of the glass. (I kind of demonstrate this at the end)