I still don't understand how to start by holding the sling with both hands.. I feel more natural to start with the sling dangling beside me, then swing it up. If I do more than one rotations, I will then hesitate and will naturally do TOO many rotations. I can't control that.

I learn from that mark weawer's video. I use slow motion to see how the moves are performed for a few times before trying out.

I can't control my moves...

I think C-A summed up my throw correctly up as a simple overhand with an extra rotation.  Rotation is counter clock wise looking down from over a right handed thrower.  I start by holding the patch and stone in my left hand with my arms relaxed and down but with the chords held taut (I use a close hold with both chords pinched between my throwing hand's thumb and forefinger... retained looped around the middle finger and the trigger a figure eight knot under the thumb).  I raise my arms extending my left hand and toss the patch toward the rear behind me releasing them at about a nine o'clock position.  My throwing upper-arm is extended about horizontal at the release with the forearm raised above my head so the chords clear my top not.  The chords are taut from either my holding them so or from the stone/patch force of rotation.  The first rotation is relatively slow as I feel the stone mass and set up for the power stroke. It comes around (again counter clockwise rotation) to again about a nine or eight o'clock position.  At that point the power is put on through the release at about twelve o'clock.  Using just the mechanical advantage of the throw I can put eight of ten balls into a ten inch circle at thirty feet.  I start easy using only wrist action and work the technique and focus on the accuracy until I get everything working again and then start to dial on the power.  I then move back and continue to throw.  If there are pent up frustrations to be released I will then add a full baseball picture's motion and really throw my whole body into it.  River bed gravel against a concrete wall (20 yards) completely shatters leaving a cone-shaped deposit on the surface of the wall.

I tried the figure eight for over fifty throws when I first read about it in the 1985 Mother Earth News.  Maybe it's just my awkwardness but I banged patch and projectile into my head multiple times.  I sat and studied the throw and thought about where I wanted things to be located when I put on the power and decided releasing toward the rear would be way more natural... at least for me... got up and loaded a stone and was suprised it felt so natural.  I have never looked back at the figure eight because my variant gave me all the power I've had with any throw and accuracy exeeding by far anything I had ever experienced... again more accurate than I can throw without a sling.

I am committed to making the figure eight work but I will not commit , at least not for now, to ever switching to it as my primary/favorite technique.

To Dravonk,
No... my effective length is now just a tad shy of one meter... 39 inches.  Again I never trimmed back to re-achieve accuracy after my last re-chording as the throw technique gave me more accuracy than I'd ever before achieved with any length chords.  When I was trying the figure eight in earnest (1985) I was using an overall length of about 30".

To C_A...,
Your sidearm throw... do you start with the patch hanging or do you release it with your non-throwing hand at the start of the sidearm windup?