>>194221totally.
if you know how to tailor your ammo to your bands, and cut them right.
I've got a mate who's had >75J out of his slingshot with the right setup, and the slingshot was the same pattern and size as this. iirc a .22lr is only doing about 85J
he did a good bit of impact testing on sheep's skulls, fox skulls and so on, the general consensus was, anything better than about 25 J will blow a skull to bits at 20m.
I've got no hesitation is saying that a 12mm lead ball 4g mass (typical ammo for rabbit hunting here in the UK with a slingshot) will drop a human with a head shot ( not a hard shot to make, we head shot birds and rabbits)
