For my Designated Marksman optics buyer’s guide, here’s the definitions I followed.
I rated the scopes’ low light capability by comparing them to a 10-year old standard sniper scope, Leupold’s VX-3 3.5-10x40mm tactical model, set at the same magnification as the test optic. The brightness comparisons were made under full-dark, moonless conditions in my back yard while viewing realistic situations: A light colored boat across a small lake (350 yards w/no street light illumination) — a full-color facial sniper target (50 yards w/distant street light illumination) — a car sitting under a street light (125 yards) — the deck of a house w/faint streetlight illumination (100 yards).
If a test scope’s image appeared brighter than the Leupold 3.5-10x40mm, I gave it an “A”, similar to the Leupold a “B,” and dimmer than the Leupold a “C.” Since all scopes are much brighter at low magnification, the grade was assigned for the maximum magnification setting.
Secondly, I evaluated each scope’s elevation and windage adjustments for both the accuracy of their values (did a ¼ minute-of-angle adjustment actually move the group that value?) and the repeatability of their adjustments (when moved four inches, did they come back the same distance when reversed?).
Lastly, how did the adjustments react to a small refinement adjustment of one or two clicks? I didn’t expect these scopes to give perfect adjustments, as I would in a sniper-grade optic, yet all gave excellent performance except where noted.
Scopes with their reticle in the First Focal Plane allow rangefinding and holdover aiming at any magnification, but since the reticle is much smaller at 1x, their usefulness at such tasks is of limited vaule. Reticles in the Second Focal Plane stay the same size at all magnifications, but are only accurate for rangefinding or holdover aiming at the maximum magnification.
Any secondary aiming point available on a scope’s reticle is compared to my standard M4 sighting recommendation for 5.56mm M193 training ammunition (55 FMJ projectile at 3050 feet-per-second): one inch high at 100 yards — which puts the load about dead-on at 50 yards and again at 200 yards.
