Bullet drop compensation

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Bullet Drop Compensation (BDC) is a feature available on some rifle scopes (sometimes referred to as elevation). The feature compensates for the effect of gravity on the bullet at given distances (referred to as "bullet drop"). The feature must be tuned for the particular ballistic trajectory of a particular combination of rifle and cartridge. There is a dial on such scopes that allows the user to turn it by single "clicks" (usually adjusting deflection or drop in increments of minutes of arc or MOA) for current conditions of distance. These scopes also generally allow for adjustments for windage with horizontal adjustments.