Holes bored into the face at an angle which may vary from 30 degrees to 60 degrees to the line of face and 6 to 7 ft (1.8 to 2.1 m) long. The distance between shot holes, the angle of the hole, and the charge, depend to a great extent on the hardness of the coal. As the coal grows harder, the burden on each shothole must be reduced by placing the shotholes closer together and reducing the angle of the hole to the face.