Concerning Staff Slings
http://www.staff.ncl.ac.uk/nikolas.l...taffsling.html
that's what I read from it (someone should check vs. historical sources)
- staff slings do more damage (due to heavier projectiles), but do not necessarily shoot further
- normal slings may carry a shield (AFAIK, historically they didn't, but would be nice in DOM

)
Concerning BigDaddy's post:
That's basically what I said before. Nice to see that someone checks the sources instead of re-telling misconceptions from Hollywood Movies ... Didn't have the time to dig anything up myself besides the Wargamers Research Groups Tabletop Rules.
Btw., those roman texts speak about
shortbows, o.c., which are roughly equal to slings.
Concerning the range, one has to be careful that not effective and maximum range is compared - what I believe is the case with the above figures.
It's very obvious, however, that slings and bows (longbows too) where used for "mass archery", not for sniping.
Xbows where used in siege warfare and as sniper weapons against (and from) infantry forming a "shield wall".
Here's a pic from the "Maciejowski-Bible" (ca. 1250 A.D. ; Piermont Morgan Library, New York), which clearly shows:
- usage of iron pot-helmets and full chain (which even covers the hands) by knights and infantry.
- the Xbow-man only has (darker) leather cap and no chain mail, he's protected by a heavily armored infantry man with shield
- the Xbow is not pressed against the shoulder, it doesn't have a rifle stock.
- Xbow is used to snipe at single defenders, obviously successful
.