I am soon going to be building a slingshot crossbow and i will be using Thera tube silver and stretching it from 20cm to 70cm (3.5 times). i am hoping for the bands to last for a very long time. So can you give me any idication of how many shots i will get??? Have you used Thera tube silver, how many shots did you get??? now to my last question what rubber will last the longest? thanks for your time.