High Quality Content by WIKIPEDIA articles! Rifleman`s rule is a "rule of thumb" that allows a rifleman to accurately fire a rifle that has been calibrated for horizontal targets at uphill or downhill targets. The rule provides an equivalent horizontal range setting for engaging a target at a known uphill or downhill distance from the rifle (called the slant range). For a bullet to strike a target at a slant range of and an incline of , the rifle sight must be adjusted as if the shooter were aiming at a horizontal target at a range of . Figure 1 illustrates the shooting scenario. The rule holds for inclined and declined shooting (all angles measured with respect to horizontal).