I get that you don't know me so I'm not going to fight with you about my qualifications. But find the velocity for any 300 gr .45-70 hollow point factory load and compare it to a 20 gr .17 Hornet v-max bullet factory load. There will be at least a 1000 ft/s difference between them and shot placement won't be as critical with the .45-70.

Masiakasaurus. I didn't mean to offend. Just a little fun banter.

Okay ladies. You are both very clever.

Heavier, to a point, has always been more efficient in my experience. I look at it as a  bell curve.  I also agree that some of the figures given about the heavier projectile being only 75% slower might be off. Maybe not if your He-Man, otherwise, not likely with your typical target slings.

It's all about sling length, throwing style and the physique of the slinger in my opinion.  I guarantee I could never throw a 7 ounce projectile at 75% of the speed of a 3 ish ounce projectile.  Just isn't going to happen.  At least not with my normal sling length. With a long enough sling though I could probably sling the 7 ouncer almost as fast as the lighter stone. Just another example of why there is no one size fits all sling length.  Tailor fit the sling length to the projectile weight, slingers physique and throwing style.  Just like you would with a bow.

From a lethality point of view, stone profile is just as, or possibly more important than a few ounces of additional weight.  A pointed three ounce projectile should probably kill a deer quite easily, as it will have the profile needed to penetrate into the deers vitals and leave a 2 inch hole in it's wake.

An interesting and long discussion.

But then I throw 50g or 500g projectile, I will let throw every straight.
(Except if I will throw the length.)

Pikaru, I knap basalt quite a bit, I know the densities change.  However, they don't change that much, if they do, they they aren't basalt anymore, they are pumice or dacite or something else. 

That's why I said that there was something wrong with Mas' picture.  Either some one messed up converting grams to ounces or someone misidentified the type of stone.  I lean towards the last, anthropologists are not geologists.