According to RatedRR, the "XS1 is the largest-caliber Precision Guided Firearm available today." This video demonstrates how its automatic targeting system works over 1,123 yards. That's one kilometre (0.6 miles). This is the kind of stuff we only imagined in science fiction movies only a few years ago.
The rifle's automatic targeting system—Tag Track Xact—can hit targets 1,200 yards away using algorithms that compensate for the wind speed. Once you put the reticle on the marked target, the rifle let's you pull the trigger and boom, your target is history—all while streaming video of it all to Android and iOS phones, where it can be recorded.