For a sling you need two bits of cord and uhh?
I had two bits of cord near at hand, being a knot tyer. Mountain boot laces. So I fiddled a bit and came up with a sling. As you can see it is a little uneven. I had never slung a ball and did not want to spend much time, effort or money on a sling till I had. You can see the picture at
http://pg.photos.yahoo.com/ph/willeke_igkt/detail?.dir=/181a&.dnm=b3bc.jpg&.src=... It is 0.80 meter, 31.5" from the fold to the end of the retention loop and release knot. On me that is heart to hand.
The pouch is 12 cm long and 5 wide. ( 4 3/4" x 2")
Then I went shopping for balls, having read the gruesome stories of some first time slingers I decided I rather throw with something soft till I know what I do. So foam balls were the safest, I found some tennis ball size (the red and yellow balls in the photos,) and some golf ball size in neon colours. I also found some children's balls about 8 cm across, a little sloppy and soft, also in bright colours. All 8 balls together weight about 180 grams, the small balls seem to weight almost as much as the bigger ones so say near 20 grams for the small ones, and near 25 for the bigger ones, (as a guess, my scales are not good enough for individual weights.)
Before leaving for the fun I had another look at the balls and the sling and decided I needed another sling. So, not wanting to use my leather for something temporary, I took a bit plastic sheet. (It is the kind called Tyvek, which we use at work, it looks like paper but is as strong as many textiles.) I had a strip 22 cm wide, so I cut a bit off at 8 cm and cut it partly in from the sides so now there is a bottom to the pouch of 6 cm with two flaps of 4 by 8 cm to each side which will slip over each other when tied. Holes in the sides, one for each bit of plastic. Another two mountain boot laces for cords, and after tying some more knots I had another sling in just minutes. Only tools needed, a pair of scissors and two hands. I have seen pictures of this style sling recently but can not find them now to give you a link.
The length of this sling is 80 cm too.
It being a rainy day in winter I went to the park and in there I found a field 40 by 50 meters with a windbreak all around it. The trees and undergrowth all leafless I could see people coming from much father away, and with the balls, even if a direct hit would not harm them, I wanted to avoid it all cost. So I went to ten meters from the end of the field and set up for the first throw. It worked, it was the sling with the plastic pouch and an 8 cm ball. It flew for 7 meters and landed in the grass. All the other balls flew roughly the same way, all landing within a few meters of each other. The small balls I slung with the all cord sling and they flew nearer 9 meters.
I had fun for an hour, improving my range to nearly 20 meters. Remember, I used the very light weight balls. When it started to rain I decided to stop, have another look for the little green ball which got lost for the second time. Walking around I saw a fist size bit of rock on the ground, it being sandy and clay ground all rock is brought in and it being a children's playfield, I felt right in taking it from the ground. I tried slinging with it and it flew, also a 20 meters at the best try. It weights 400 grams. But I did not dare to try a throw with anybody within seeing range through the trees.
I had a few miss fires, with the balls as well as the rock, but no problems, nothing damaged.
Now I know I want to make a proper sling and have another go.
The sling with the plastic pouch did well for the biggest balls and just not good enough for the tennis ball size, and the all string sling did work for the golf ball size but at times rather unpredictable. The cup is not smooth enough. I think it will do if caught out with a limited amount of string and nothing to make a pouch but I would try to make a proper pouch if possible.
More photos available at
http://pg.photos.yahoo.com/ph/willeke_igkt/album?.dir=/181a&urlhint=actn,ren%3as...If the direct links do not work go to the album sling.Willeke