Abstract: Disclosed herein is a rotary-percussion earth boring bit that has an improved geometric configuration to extend cutting insert life and reduce cutting insert breakage. The bottom surface contains a flat transverse face with a bevelled edge. Two rows of circumferentially spaced cutting inserts protrude from the bevel. One of the rows is spaced inwardly from an outer row to define an inner row, which has inserts positioned between the circumferentially spaced inserts of the outer row. The longitudinal axes of these inserts are substantially perpendicular to the bevel and inclined outward at an acute angle to the axis of rotation of the bit. A generally longitudinally extending groove is formed between each two adjacent inserts of the outer row. This arrangement produces a symmetry that tends to minimize the number of reflective surfaces. This equalizes the stresses generated by the impact induced shock waves transmitted through the bit.