Why Does My BAS Reticle Need To Be Used On A Specific Magnification Set?

Leupold Ballistics Aiming System reticles such as the Boone & Crockett Big Game, Varmint Hunter’s, LR Duplex, LRV Duplex, S.A.B.R., Ballistic Firedot, Multi-Firedot, Pig-Plex, Impact, T-MOA, or the Custom, Ballistically Matched reticles are typically installed in scopes with a rear focal plane design; allowing the user to tune the reticle for use with multiple loads. Changing the magnification in rear focal plane designs changes the subtension of the reticle, effectively changing the amount of holdover provided by the long-range aim points of these reticles. This can be observed by placing the main aim point (crosshair) in the center of a target, changing the magnification, and observing the resulting effect on subtension. The observer will notice that though the main aim point remains in the center of the target, the holdover points appear to move up the target as magnification increases, and down the target as magnification decreases. As such, faster loads with flatter trajectories will require a higher magnification setting than slower loads with more bullet drop. It is important to note that since the main aim point is located directly in the center of the field, it does not move as the magnification changes; this allows users of these reticles to sight-in on any magnification setting.

One example commonly used to help visualize this effect involves viewing a deer 400 yards away with a fictitious scope ranging from 1x to 100x. If the scope is set to 1x magnification and the main aim point is placed directly on his shoulder, the deer appears rather small and occupies very little of the visual field. Because the deer appears small and only occupies the very center of the field, the 400-yard aim point is located well below the deer, representing many feet of drop. As the magnification is increased, the main aim point remains on the deer’s shoulder, but he begins to fill more of the visual field. When 100x is reached his shoulder fills the entire visual field, placing the 400-yard aim point only inches below the main aim point. The result is that as magnification is increased, the target begins to fill more of the visual field, making the holdover points appear to walk up the target, thus representing less drop. As magnification is decreased, the target gets smaller, making the holdover points appear to walk down the target, thus representing more drop.