Just for starters, if you moderators want to move this to other topics I would understand.  Now that I have that out of the way...

Alright, here are the standard rules for the sling in 3.5 rules.  A sling is a simple ranged weapon, that does 1d4 damage, and has a range increment of 50 feet.  The maximum range of a projectile weapon is 10 times the range increment, with the difficulty increasing by 2 for each range increment past the first one.  This gives you a -18 to hit at your max range.  The longbow in contrast does 1d8 damage, with a 100 foot range increment.  Now doing the math, this means that the maximum effective range for a sling is 500 feet, or 166 yards, while the longbow's is 1000 feet, or 333 yards.  The main advantage that the sling has over the bow in D&D rules is that you can add your strength modifier to the damage with a sling, but you can't with a regular longbow.  With the sling you must use manufactured sling bullets for full effect.  You can use stones, but you take a -1 penelty to your attack (they are less accurate).

My house rules up the damage of the sling to 1d6 (plus strength modifier) for stones (-1 to attack still applies), and 1d8 for lead glans, with a range increment of 120 feet (max range of 400 yards).  I toyed with the idea of requiring an extra feat to be able to use the sling, but decided against it.  Loading still takes a move action, though you can take a feat to be able to load it as a free action. 

So, what rules do you guys use?

that also brings into question....

how much work do we allow the leverage and mass to do rather than our own muscle 'oomph'?

Thanks guys, now  want to play D&D. Time to crawl into the basement again...

played a bit when I was at college - then they invented home computers and I didn't have to play with the other children
Dungeon master on the atari st was the business ! (20 years ago lol)