Abstract: The invention is concerned with pneumatic percussion drilling equipment with advantageous manufacturing simplicity and effective piston area to casing size consisting essentially of an elongate hollow casing housing a piston assembly and having a backhead at one end with a compressed fluid inlet, a bit assembly with a compressed fluid exhaust at the other end, and the backhead including a seal for a backhead end of the piston reciprocatable within the casing, the piston having axial bores extending inwardly from each end, inclined passages extending away from the inner ends of the axial bores to open through the wall of the piston at positions axially displaced from each other and towards opposite ends of the piston from their respective axial bores, and the casing walls having axially spaced apart recesses, the backhead seal, casing recesses and opening through the wall of the piston being such as to allow fluid under pressure introduced axially into the casing through the backhead, to reciprocate and to mai