Hobb i use 5 mm nylon cord, it's made of a core of nylon fibers and an external layer of braided nylon , pretty much like climbing cords, (we use this cord to hang hogs at the slaughterhouse, and they stand up to 300 pounds)
I just use 3 of this cords (about 6 yards each) starting to braid from the middle, 1st i braid the finger/s ring with 3 strand braid, then i join the 3 strands of each side to close the finger/s ring and start braiding the retention cord (3 couples (6 cords) strand braiding)
once i get the desired lenght of retention cord i separate 3 cords each side and start to braid 2 separate 3 strand (single cord) braid for the split pouch.
once i get the desired lenght of pouch i join again the 6 cords and start to braid the release cord (3 strand braidof 3 couples of cord )
When i'm getting the desired lenghth i trim one of the central couple of cords, i burn (melt) the cut zone so fibers don't desinteger and i sew it to it's fellow with a strong thread i con tinue braiding 3 strand ( now there is only 5 cords, two couples and one single ) and after i've braided about 10 cms i trim again one of the central couple of cords... again burn the cut zone and sew it to it's fellow... then continue braiding (now there are only 4 cords one couple and 2 singles) continue braiding for another 10 cms or so and trim again one of the last couple strands when it's in the center of the braid,... again burn the cut and sew it to it's couple... and continue braiding 3 single strand braid for another 10 cms or so, then sew this 3 strands together and desinteger some of the fibers to make the end fluffy tail (this will make a CRACK! sound when slinging, like a whip.
And that's all... i'm planning to post some pics step by step so anybody can make his/her own sling... it's easy and quick to make
^ Here you can see the whip-like end of the releasing cord, note the 3 central stiches where the central couple strands have been trimmed one of its cords, and the final sewing and around tie before the fluffy end.
^ Here you can see how the split pouch is made... 3 strand braid of 6 cords (3 couples) is separated into 2 braids of 3 single cord each, and then join together again when the split pouch is done.
This is the traditional way slings are done here (shepards used natural fibers, mainly pita (agave americana) or any other strong enough at hand hemp, linen etc...) remember... as long as it has a pouch and a retention and release cords it's a sling