I think that the release cord should be light. The stone has to open the pouch against the inertia of the knot end of the release cord where the speed is much slower and so centrifugal force to self-open is less.

Also, when the stone hits the release cord as it often does, you want it to be light to avoid deflecting the stone.

I've only experimented a little with this but I've found that with a uniformly thick and heavy release cord the release itself gives an unpleasant jerk to the hand as the cord snaps fully open. The beautifully tapered release cord on the Balearic sling I'm pretty sure is designed to minimise this and acts like a cracking whip where the wave pulse accelerates down the length of the cord as the mass per unit decreases. This should give the best of both worlds with a quick snappy release without the jerk of a heavy cord and the tangling problems of very thin cords. Of course tapered cords must be individually braided which excludes using commercially made cord cut to length and complicates sling making greatly. BTW Interesting to note that the Tibetan slings that seem so popular at the moment don't appear to have this tapered release cord feature.

On the pictures I saw here, I always had the impression that the balearic slingers used rather thick cords. That is the reason I got the idea to use a thick and therefore relatively heavy release cord.

But then on my last slinging session I always had the impression that the bullets went too much down. I also used another sling with a thin release cord this day with which I was very accurate. But each time I used the sling with the thick cord I had to aim much higher to hit the same spot on the tree and had  to use much more force.

Now I found a thin polypropylen cord which is also rather stiff. I have exchanged the thick cord with the thin cord. Thick cord: 16g. Thin cord: 8g (in fact in both cases there are a few gramms to add for the chain knot I have bound at the end of the release cord - for this I use a thin cord).

Now both slings give the same results. With both slings I hit the spot of the tree I want to hit without having to aim higher or lower.

The weight of the retain cord does not seem to matter.
One sling has a retain cord of 26g (aramid) and the other has a retain cord of 16g (polypropylen ).
But I have the impression that I feel the difference of weight when slinging.

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So my old philosophy still holds: Make the sling cords stiff if possible but not at the expence of a higher weight in the case of the release cord. For the retain cord the weight does only matter for the whole weight of the sling but not for the direction of the bullet.
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