I didn't use springs, I used 1" o.d. Seemless pipe which has an I.D. Of 1/2" . The trick to making them work right at different distances and with a variety of ammo is adjustable tilt... I used a turn buckle and hinged the bottom... If the targets swing around and bounce back at a given distance/ammo combination, adjust it so the tree is more vertical, if they come part way up and fall back down tip it forward slightly... Also I used 1/2" bolts with a slight angle for the pivots.



















































