NOTE: I am not responsible for any damages, injuries, etc that are a result of sling construction or use.
Step 1: Materials
For this instructable, several things are required. A material for the pouch, cordage for the lines, leather scraps for a handle, something to cut everything, and something to make holes.
Pouch: It can be anything, really. In my opinion, leather is the best, or perhaps a woven pouch, which is not covered in the following directions. Any cloth will work, with varying degrees of durability, leather being more so than most types of cloth. I have cut leather from old shoes and an old backpack; I also get various bits and pieces from a local shoe store (the kind that makes and repairs shoes, not a shoe retail store). Leather can also be obtained at thrift stores in the form of old coats, bags, etc.
Lines: Simply because it is on hand, I use hemp. More specifically, I use braided hemp, which is braided and not twisted because a braid tends to have lower elasticity than a twist. Like the pouch, the material used for the lines can be really any type of cord. Hemp, linen, cotton, nylon, leather, wool, other natural fibers, other man made fibers, gut, etc. Realize that some materials will have more of a propensity to stretch under strain than others.
Handle: Scraps, roughly oblong, which can be made of anything.
Cutting utensils: Self-explanatory. Scissors, knife, etc.
Hole punching: A paper hole puncher will work on some leather. A leather punch works well. Scissors or a knife can make holes, albeit with more trouble and less tidily. Use your imagination.
Step 2: Pouch
The pouch can be cut to different dimensions and shapes, but I usually use a basic design tailored to the amount of material I have. As seen in the picture below, the pouch is an elliptical shape with wedges cut into the ends. The resulting flaps need to have one hole punched or slit in each flap. On slings I have made, the pouch can be 2.5 inches wide or 7 inches wide, and 2 inches tall or 3.5 inches tall. From that statement, realize there is a large variance in pouch size.
One thing to be aware of: if the pouch is too small, it will be difficult to keep whatever projectile is being thrown in the pouch before release, because the center of mass is above the line attachment.
Step 3: Lines
At either end of the pouch, a length of cord will be attached. The length of these lines can also vary; I have one as short as 18 inches and one over two feet long (per side). Many people make them even longer.
As previously stated, braided lines are more ideal, simply because they stretch less, making the sling more accurate, but twisted lines will work also. Manually stretch twisted lines to help negate the stretch factor. I have used both twisted and braided lines, with both working well. One of my slings with twisted lines utilizes an old bowstring I had made but broke, so it was rather inelastic due to the stress of the bow.
Make sure enough cord is used. At both ends of both cords, tie a small loop, or braid a small loop and connect it back in with the main part of the line. On one line, attach the scraps for a handle. Push the loop through holes or slits made in the scraps, and feed the other end of the line through, pulling tight to affix the handle to the line.
Step 4: Attachment
Attach the lines to the pouch in the same manner the handle was attached to the lines.
Step 5: Use
On the line without a handle, push a small amount of cord through the loop to created a slipknot. Fit this slipknot over any of your fingers (a thumb is not a finger because it has one fewer phalange than the other four appendages on the average person's hand). I use my middle finger. In the same hand, pinch the handle between the forefinger and thumb. Place a projectile (rock, shot, hand made cement or clay ammunition, etc) and with what amounts to a swinging motion, fling the projectile. Release the handle at different times, point yourself in different directions, or swing the sling in a different plane to aim. It is quite difficult to use one accurately.
Please excuse the poor directions. To articulate with letters on a page the actions required to fire a sling is not easy, so for the convenience of myself and the reader, please follow these links that demonstrate how to use various slinging techniques. Thanks to youtube and the members who supplied the videos.
Greek Slinging: http://www.youtube.com/watch?v=vBh2B3oeKtM&playnext=1&list=PL22AED7B6637E61F4
Byzantine Slinging: http://www.youtube.com/watch?v=dHDAXa_-gC0&playnext=1&list=PL5E6DAC09D661E7E5
Apache Slinging: http://www.youtube.com/watch?v=YHXCd4eCrxk&feature=related
Figure 8 Slinging: http://www.youtube.com/watch?v=_PyN2MnBOzI&feature=related
Step 6: Completion
Thank you for viewing!