One of the many translations gives me the following

'''...sed triplex scutale, crebris suturis duratum, ne fluxa habena volutetur in iactu glans...''
'''...but a triple pouch, hardened by frequent stitches, lest the loose strip may be rolled in the shot of a bullet...''

Lest the loose strip...are they talking about the release cord (=loose strip) here rolling into the way of the projectile or rather the projectile rolling into the release cord?

''...sed librata cum sederit''
''...but in balance when he shall give''

It is a very interesting passage.

Did the balearic slings looked the same as they do now?
were they braided fibers or leather straps? so we can understand what the writer compares

''ne fluxa habena volutetur in iactu glans..''
''lest the loose strip may be rolled in the shot''

Again we see the word ''habena'' which is a form of ''habenae.''. It makes sense
that a ''strip'' or rather flat and/or thick release 'thong' can interferes with accuracy as the ''bullet'' can roll into it causing deflection. I'd never pick my all leather slings or flat wide braided slings for slinging glands either.

Could it mean the Achaean sling was really just a conventional sling, with lets say, a 3 strip leather aussie pouch, with cords sewn to it? Round cords, compared to flat thongs. But what strikes me as odd is that I can't place this model of sling as being special, it must have been used by other nations right? It's not like the Achaeans invented cordage.

it does lend itself to the Y-sling theory and it could be true. The problem with this is that there is just zero hard evidence, no historical findings I have seen that resemble this sling. There was one historical sling with a ring pouch and 4 cords but that is not a Y sling. I have seen conventional slings with 4 cords but the space between the two release cords is too narrow for most stones and it causes erratic behavior, sometimes they fly through the cords other times not. And here is not talked about ''quadruplex'' but ''triplex scutale''.

At the same time it could be that the Achaean sling was simply a conventional sling but with a more dedicated pouch and cords. It is likely. The problem I have with this is that it hardly can be considered unique because we have such slings from many nations and places all around the globe. 

Who is the author of this text ?
I'm agree with Sarosh.
Your reasonning is based on your assertion that the balearic sling was the same of today. Which is just an unverifiable assumption.
Habena may be made with leather. Like this one.

Hmm, so Achaean, basically Greek.
As with pretty much all Latin texts the problem is with the translation.

And it's just occurred to me that I do know an Oxford graduate Latin scholar.

I'll have to get Isobel's email from her mum and drop this across.

With it being Greek, it could be anything, they had every material and technology available in the ancient world.

Where's this quote actually from ?