0d6 Damage?
I checked and it's correct: this sling should cause only acid damage damage when used without bullets. It says "Damage: 1d6+2 (acid)" which says everything is acid, no other type of damage is mentioned. It's not "Damage: 1d6 (missile) +2 (acid)". And missile damage is set on the bullets themselves - check bull01.itm to check it.
0d6 is the sling damage (missile), while acid damage is introduced in "Item ability" => "Effect 0" (if you're using NI) or first effect on the list, if you're using DLTCEP to check the item file.
0d6 is the sling damage (missile), while acid damage is introduced in "Item ability" => "Effect 0" (if you're using NI) or first effect on the list, if you're using DLTCEP to check the item file.