How about 8mm steel balls for 0.8 rubber band?

8 mm steel ball with 0.6 large rubber band, 8 mm steel ball had better use 1745 round rubber band, 8 mm steel ball mass is relatively large, rubber band is extended to the middle distance of 80 cm to 90 cm. It is necessary to ensure that the initial velocity of the steel ball reaches about 70 meters per second, and the distance of the steel ball at about 20 meters cannot have obvious parabola, so as to ensure that its accuracy and effective range can reach about 35 meters to 40 meters.