A rear aperture sight for use in conjunction with a front sight post sight on a rifle. The front sight post has a horizontal top edge and vertical side edges. The rear aperture sight comprises a rear sight adapted to be mounted on the rifle. The rear sight has a horizontally elongated aperture formed therein having height and width dimensions. The width dimension is greater than the height dimension. The aperture is defined by two circular segments s1 and s2 having chords c1 and c2, respectively, defined by included angles .theta.1 and .theta.2, respectively, of circles having radii R1 and R2, respectively. The chords c1 and c2 have heights h1 and h2, respectively. Radii R1 and R2 and angles .theta.1 and .theta.2 are selected such that chords c1 and c2 are of equal length. The circular segments are positioned such that chords c1 and c2 are co-linear and oriented horizontally.