Very cool slings,and a LOT of lead You should try to make a gang mold so you can cast many glans at once. Also as lead is expensive,if you could find a nice big wall,were you could sling lead,you should be able to find most of it.If you sling them for distance,i would advice you to paint them black.You can see them much better in flight,and longer,as if they were grey lead.If you start mass producing glandes i would also suggest doing it outside,maybe wearing a mask ,and definitely put on some rubber\leather gloves when you cut of the sprue from the lead.If you cast a lot of glandes,and cut a lot of lead,handling will make your fingers black from the lead,and it's bad for ya.
One last suggestion.Make the mold to fit perfectly,otherwise you have to cut a LOT of flashing,and it goes MUCH slower,and handling lead for long is bad,hence the gloves suggestion.

I have played around with the size and shape of the split in the pouch and i have found that it makes quite a difference.

I slung a smooth (+- 80g) stone at a target today and, the moment i released, i could see it turn and spin. It had a really flat trajectory and i hit a 50 x 75cm target from about 50m away with enough force to knock a huge dent in the 3mm ploastic sheet and a dent in the plywood backing.

This sling has a longer slit that is a 1/3 of the pouch's width. I am also finding that softer leathers and longer, 1/3 width is increasing the spin. I think it has something to do with the way the sling hugs and conforms to the shape of the projectile.

I am experimenting with a few types and will take some pics of a pellet in the slings and put them on in the next few weeks.

Huge fun

What are the dimesions to this? I am gonna try my hand at making one.