How heavy a bow for 9mm steel balls

3 pound pull slingshot. The larger the draw distance, the less tension you need. I pull to 120 cm or more, 9 mm steel ball only need 3 pounds of pull force slingshot. The bow is the oldest type of catapult weapon among projectile weapons. By the elastic bow arm and flexible bowstring composition, when the pull string tension bow process of the accumulated power in the instant release.