Here is an easy sling to make. The pouch holds the ammunition securely without any interweaving.
I first made one like this based on a book I had when I was a mere youth.

It is a modified sheepshank


After 5 loops (6" long") are made you begin a sheepshank but complete an overhand knot by placing the end of the cord through all five loops and pull tight. Repeat at other end. . The source for the sling is "Whittlin', Whistles and Thingamagigs" ISBN 0-8117-1882-2. Tony