hm, actually maybe I am mistaken, because I could have sworn it was the loading property that specified the use of a free hand to reload. I've just re-read it. Sorry about that.
EDIT: Okay, I see where my confusion is happening now.
The first printing of the PHB had this passage for ammunition:
Ammunition. You can use a weapon that has the ammunition properly lo make a ranged attack only if you have ammunition lo fire from the weapon. Each time you attack with the weapon, you expend one piece of ammunition. Drawing the ammunition from a quiver, case, or other container is part of the attack. At the end of the battle, you can recover half your expended ammunition by taking a minute lo search the battlefield.
If you use a weapon that has the ammunition property to make a melee attack, you treat the weapon as an improvised weapon (see "Improvised Weapons" later in the section). A sling must be loaded to deal any damage when used in this way.
But the seond printing says this:
Ammunition. You can use a weapon that has the ammunition property to make a ranged attack only if you have ammunition to fire from the weapon. Each time you attack with the weapon, you expend one piece of ammunition. Drawing the ammunition from a quiver, case, or other container is part of the attack. Loading a one-handed weapon requires a free hand. At the end of the battle, you can recover half your expended ammunition by taking a minute to search the battlefield.
If you use a weapon that has the ammunition property to make a melee attack, you treat the weapon as an improvised weapon. A sling must be loaded to deal any damage when used in this way.
There's the extra clause. Slings were able to be used with shields, but no longer.
