Hallo there people!
I've been to the Archaeological Superintendance this morning, and asked the kind librarian to help me in finding anything related to the sling, used by ancient Romans.
She find a paper in which glandes inscriptions are described; at page 5 there's a picture of a lead glans improved with a couple of bronze "wings".
Here's a small and bad quality picture taken from the pdf I have:



The bullet has been found in Cyprus, and I personally believe that it's quite ancient, perhaps IVth Century b.C.?

Sources are:

"S(hort) M(essage) S(ervice) ante litteram - antichi proiettili iscritti e insulti di guerra", A. Naspi and E. Radaelli, inside "FORMA VRBIS" #2, Feb. 2011, Editorial Service System;

"Lead 'slingshot' (glandes)", T. Rhill, inside "Journal of Roman archaeology 22", 2009, pages 146 - 169.
Hope it helps our project Goliath  

Greetings,
Mauro.

I've never seen anything like it. It's photographs like this that keep me wanting to do more research into slinging.

I wonder what kind of sound it will make when you throw it?

I also think it's not so difficult to make.... just wait until the storm we've here in my town passes away, and I'm going to make a couple of these bullets... will show you pictures 
Greetings,
Mauro.

I'd also say it's more likely to be an anti-armor round. The increased complexity of the shape just adds more area for air resistance to muck things up, so I think it would be pretty unstable unless thrown in a spiral.

I've actually been wondering about the potential for armor piercing rounds myself, or at least increased penetration rounds. I've been making clay glans for a while now, and I've thought about setting a chipped stone point into the clay at each end. Has anyone tried something like this?

To tell the truth, my opinion is that such wings improve the penetration's power, but also the damage: a winged arrowhead causes a wound as large as its wing's length, so I believe such a glans would act the same way, given that it reaches its target with an angle of 90° or so.
Greetings,
Mauro.

I'd think the wings would cause drag, making the glans hit with the other end forward. The wings might be there to increase the amount of damage the glans caused to soft targets.

Nice find Caldou!!
So it's different - and much easier to make - than what I thought at first: a piece of copper alloy with (probably) a hole in the middle that will allow lead to spread on both sides!
I've got to make it!!!!!
A Thousand Thanks!!
Mauro.