I’m definitely not a technical type of slingshot shooter???????? I don’t follow any certain formula for length or strength of tubes. In fact I just shortened my 1632 tubes to 7 inches, opposed to 8 inches previously. So far it’s a great setup. I rely mainly on the forum members to keep me updated on helpful information. I just read a very helpful post on removing constricter knots. That will definitely help me changing tubes and reusing the pouch.???? they suggested a sewing seam ripper???? Thanks to everyone for sharing their helpful information on slingshots.