Hi kid.
Lets try.
Presuming you are right handed.
The sling is in your right hand (held just under the rib cage) and you are holding the ammo and pouch with your left hand (horisontal to the ground and the cords facing lenthwise in the direction of the target. Let go of the ammo and pouch wich will make it drop in an arc towards the ground. You have to trace the same arc with your hand and arm. As the ammo and pouch go past your right leg and as it pass lift your hand and arm to almost behind your head, slightly twist your wrist to the left, making the sling complete one full rotation to the left of your body. As it circles behind your back feel how the sling generates momentum at the pouch wich is your que to prepare for the cast.
I would also suggest that you first try without a sling.
Extend your right arm straight out in front of you (direction you are looking). Keeping it straight let your arm come down past your right leg (elbow facing towards your body) and to 180 degrees to where it came from. Bend your elbow at this stage and from behind your head, touch your left ear. You will now notice that your hand can not go down from your ear mich futher and that you have to twist your wrist to make your hand come diagonally agross the back of your head (left to right) and extending your arm to the original starting point.
It also helps if you look at the pouch through as much of the cast as you can. Notice how your head is making a figure 8. (do not do this with ammo in the pouch)
Hope all this long windednes helps.
Coenie