Rebel, ...welcome to the forum.   Re the glandes, ...there's a ton of info here covering molding these.  'Jurek' is probably the expert.  Re your technique, it sounds like the 'Greek' technique & there are a couple slingsters here who use it a lot.

The size of the orifice through which the lead was poured determined the size of the ball formed.  Also, I suppose the temperature of the lead being poured insofar as this would affect viscosity of the liquid.

After cooling and forming during it's drop through the air, the lead balls hit water for final cooling and cushioning of the fall to prevent dents, etc.

Manipulating viscosity & orifice size is the exact technique still used today to set the size of tiny superglue drops used in the assembly of electronic and similar equipment.  Also, to set the particle size for powdered milk and similar materials.

More hint to increase accuracy, having to do with design of the sling itself:

* The sling cords have to be large enough diameter and stiff enough so that they won't momentarily tangle on the ammo as it leaves the sling.

* The joint between the sling pocket and the release cord has to be absolutely smooth, so the ammo can slide out of the pocket with no hesitation.

* The preferred grip is close, ....Apache or similar.  A wide grip lets the ammo "rattle around" in the pocket, and requires use of a larger pocket.

* The pocket should be absolutely as small and flat as possible, and still retain the ammo.  Again, no pocket suitable for a wide grip is small enough.

Conclusion, ...all my slings with pockets made of crossed straps, joined to the cords with fat loops, have to go into the trashcan.   Thanks to nwmanitou for letting me try one of his fine slings.

I dont like a long release cord myself. a short length between thumb and forefinger is enough for me.