One possible reason may be the way you hold the sling.

I put the fixed end loop over my middle finger, and then pass it over my ring finger then down between my ring and pinky, palm facing up.  Then I grip the other cord with my thumb and the edge of my pointer finger.  This keeps the cords seperate, and I've never had a problem with tangling.  That's how I hold the sling in my tutorial.

Another reason is the length of the sling.  If you're doing the release I do, the ideal length (for me anyways) from the middle of the sling to the end should be about the same as your nose to the middle of your hand held out away from you.  I've noticed that when I use different lengths, it affects the timing of my release.

Mark

Grip, pouch, cords, sling length, and ammo weight all work together.  I find that a wide grip such as Mark's, works well with a sling that has a longer pouch.  If my pouch is short, things roll off the end of the pouch and result in a very bad cast (like, straight up or behind me).  A narrow grip works well with the Apache style, which has no windup at all, but if I try a helicopter style I can get my cords twisted together.  Pre-twisting my cords the opposite of what they want to do, can solve that problem.  So can using a sling with thicker braided cords (gets rid of twisting altogether).  My shorter slings just do not work well with the figure-8 style (or any other style that involves a couple of twirls), but my longer slings do not work with the Apache style.  And after I've cast something heavy like a lacrosse ball, slinging a tennis ball always goes off (usually into the ground due to "late release" -- I released same time as I'm used to, but the lighter sling load swung 'round faster!)

What is really fun (for bystanders) is when I get my cords exactly in line with the tennis ball.  The ball rolls down the entire length of the release cord, with a loud zipping sound, and falls to the ground a few feet in front of me.  I did not know what was happening until one rainy day, the dog was retrieving the ball for me and it was getting more and more muddy ... and then that zipping sound, even the dog is laughing at the ridiculous distance, and I found that the release cord was muddy all the way down its length.

Mostly I just try to learn the peculiarities of each sling I make, and use a style that works with that sling.  If I wanted to stick to just one style, I would probably also make just one kind of sling... but I have more fun trying out everything I see described, and everything I can think of.

I tryed changing my grip, but it really does not feel right. So I started thinking about the friction at the point of release, and how to reduce it. I tryed putting a piece of plastic tubing on the first 8 inchs of the retaining cord, and it has made a dramatic improvment in my accuracy.

The super narrow...???  I loop the retained cord around my middle finger and trail it across my index finger right next to the release cord so it too is squeezed by the thumb until the moment of release.  My release cord has a figure eight knot to aid in good retention of heavier missles.  I've never considered the setup a problem and think I get good-to-excellent consistency of the release.  I do confess I have never tried wider holds because of my satisfaction with what I do... it seems to work for me and my sling design.    I do know if I do anything more than "two rotations and out" that the cords twist and the release consistency gets way messed up.   Maybe someone will tell me just what are the reasons for going to wider releases...???