Terrific discussion! I'll add comments that apply to many of the posts above.

I have made a glandes mold from aluminum, they are football shaped.

Research shows that most Roman glandes were 24-25g. Very small. I think the multiple glandes idea is viable, but still not proven.

One theory for the elongated shape is that they stay put in the pouch better than a sphere, making for faster spinup.

Researchers label glandes as Type I (football) and Type II (acorn). I think they are wrong. I think there were all double pointed. The so-called 'acorn' shapes were merely a double-pointed one that struck something hard and squashed its point. No description, drawing or mold for an acorn shape has been found, as far as I know.

Pouch release does indeed spin the projectile, my observation says.

A flat shaped glandes will 'buzz' when thrown and spun.

My theory for the flattened shape is that they wanted the 'buzzing' when they fly. Hannibal said his elephants were annoyed at the buzzing of slingstones.  The torrent of slings was used by generals more to break discipline and induce fear in the opposing troops than to do actual damage. It they heard the 'buzzing' of a near miss it would have almost the same effect as a hit. Very demoralizing, and very effective.

I have been checking bookshops today in Kuta, and haven't found the Guinness Wolrd record Book (for the slinging picture) yet.  Some stores were on back streets before, and I haven't been able to find them yet.  Stores here often open and close and reopen again sporadically, so it's hard ot tell whether a business is still here, but I may also have seen the book in Yogyakarta on Java, and I always visit both islands, so I'll look there, as well, and then look again here when I return on my way out if I don't find it here the first time.  I'll also see, about the camera, etc. for the picture of what I like to use personally to sling rocks and bullets/glandes.

I have found that slinging three egg-sized rocks or three-to-four oz lead egg-shaped fishing sinkers is very effective from a fairly large-size triangular net pouch (about the size of my hand, only about half longer).  When throwing very large bola-type weighs (+/-10 oz.), I only need two of these projectiles to give me the lateral spread advantage of a "shotgun" effect, but if hunting with the sling, I would recommend using the three 3-4 oz.-or-so stones.  They group and triangulate well, covering a reasonable area to increase multiple, or at least single hit probability out to several meters.  Since small game is generally engaged at pretty close distances, especially with primitive weapons, I would use a shorter 1.5-to-two foot sling, and a simple over-the-back centerline-preserved hanging carry while stalking the animal, with the pouch and stones/bullets resting dead center of my spine and near the small of my back, or slightly higher, and my thumb resting somewhere near my "rooster tail" crown or the center of the back of my neck.  Then, when the time came, I would bring the slinging hand straight up overhead, then arcing down violently when the pouch had cleared the back of my head (OUCH! if you don't!  you have been WARNED!!!), my knees bending, my front foot bending in a "falling" trigger step (as when executing a proper left jab in boxing to bring the body full weight violently forward, adding most of the force to the punch, or when using "gravitational marriage" when throwing a knife or spike) and bowing violently from the waist through the release, and bringing the throwing thumb directly down my centerline past the spot a couple of feet in front of the tip of my nose.  All of this not only maximizes the power of the shot, but cuts the throwing/movement time down tremendously to prevent spooking the game/alerting an attacker thant you are not just scratching the back of your head or rubbing your neck, takes full advantage of instinctive gross motor movements in a self-defense or "deer/buck fever" situation when fine motor skills tend to go "bye-bye!" and is safer since it makes it harder for the stone(s) to fly out prematurely in a harmful direction with any power, thereby harming anyone or anything seriously.  Furthermore, it increases the chances of consistent throwing, since the gross movement at the waste, shoulder and elbow is harder to unintentionally vary, deviating from the centerline.  Therefore it is easier to concentrate on the vertical release timing, and therefore, tends to leave only the vertical timing/aiming point as the only remaining major variable in the equation.  I have cut the training time and increased the safety factor tremendously when teaching new student slingers this method.  But I use it, too, and would tend to prefer this method for many situations, anyway.  It also gives the slinger a GREAT physical workout in all the right places for several other sporting activities, as well!

Dear Yurek,

Thank you for the encouraging words!  I usually like to use my longer slings, and go for maximum power and range, but lately I've been using the shorties more, because for quick response situations, I think they are the most practical.

I think I can see why the best slingers from some ancient countries carried three slings:  the short one for short distances (I also think a quick single underhand shot with a short or medium sling can be very effective in the same situations, but requires more practice to be accurate with it.  I could smash rocks into pieces against boulders using both of these throws even with a short sling and no windup in the case of the overhead "bowing" throw, which surprised me), a long one for extreme range and a medium length one for general use.  Of course, you are living proof that the longer ones are best for making the longest shots.

I think that the medium length sling offers a great compromise between the advantages of long and short slings, and is probably the most versatile sling to use for all but the longest, or conversely, the quickest close range shots.

The short one is probably the quickest and easiest to bring into action in a close-in defensive situation in combat, so it would make sense that even the top slingers who could throw hundreds of yards with a longer sling would still keep one handy as a sort of side arm.

One could be carried in modern times into a stressful and potentially dangerous situation (as a better alternative than being unarmed and defenseless) undeneath a jacket slung casually over the shoulder "rat pack" style, but pinched between the index and middle fingers, leaving the thumb and index fingers holding the release node and retention cord.  If things escalate, the jacket can simply be allowed to drop back over the shoulder and fall to the ground, leaving the short sling unobstructed, and ready for instant use, if neccesary, using that "bowing" throw mentioned above, or maybe a quick sidearm shot.

For Yurek:

I would suggest you try some nylon commercial fishing net and net line.  There are many kinds and sizes of this stuff, and you can get some that is very light and doesn't drag perceptibly.  It is stiff enough to avoid tangling, and yet comfortable enough not to hurt your fingers.  Being made to resist snagging on razor-sharp rocks, it is extremely durable.

You can use the thickness that is about the same as twine, and choose among many thicknesses within this range.  For the pouch for a long distance sling, I use about .5-to-1 cm. per square mesh woven nylon net of about the half-to-twice the same thread thickness as the cords.  It doesn't much matter, because this stuff is SO lightweight and strong, and drag is so low as to be practically a non-factor!

Cut the pouch into an oblong square almost the same size as the glande when wrapped around it, but a little longer, so that it will stay in the pouch.  This can easily be done through trial-and-error!  Tye the retaining cord to the near end of the pouch by weaving it through the mesh squares, forming a "scoop" shape.  ONLY tye the release cord to the CENTRE mesh thread/cord, or if off-centre due to an even number of squares used, to the thumb-side square thread/cord nearest the centre of the pouch.  This will result in a roughly triangular appearance to the sling, which will allow it to open up well on release.

If desired, you may also trim the "wings" or release-end corners of the triangular sling further to decrease potential drag, and return symmetry to the shape of the pouch, but this may affect the retention factor somewhat, depending on your particular winding and release technique.  BTW, I noticed that you seemed to be using a "full fist" grip on the sling with a pinky grip on the release node/cord. 

I personally find that greater power may be added by changing to a between- the-thumb-and-forefinger "pinch" grip, and using a wrist loop to take felt pressure off of the fingers of the throwing hand.  It seems to allow for an "looser wrist", allowing for faster accelerating rotations on the windup strokes than other methods I've tried.  You may also wish to experiment with different types of light gloves and cord thickness combinations.  Good luck on bagging that world's record, once again!