Weapon (sling), common
A small strip of cord wrapped around a nocked arrow that is whipped forward for extended range and accuracy.
Proficiency with a Sling allows you to add your proficiency bonus to the attack roll for any attack you make with it.
This weapon has the following mastery property. To use this property, you must have a feature that lets you use it.
Slow. If you hit a creature with this weapon and deal damage to it, you can reduce its Speed by 10 feet until the start of your next turn. If the creature is hit more than once by weapons that have this property, the Speed reduction doesn’t exceed 10 feet.
Notes: Weapon Property: Loading, Ammunition, Range, Slow
cool
you can't knock an arrow in a sling, you say that it gives more range but don't state how much more and there is no mention of aarockocra in the description so you clearly just added it so it would appear in front of the others.