In your weapon prefab, look in the First/Third Person Shootable Weapon Properties section for Reloadable Clip Attachment ID. Set a value there, then go into your player and add an Object Identifier component to the object you want to assign and set the same value there. I actually just set up a bow pickup, so I specified a value of 1 on Fire Point Attachment Location ID, dug into the hierarchy on my player to find the arrow attachment object, clicked Add Component, added Object Identifier, and set a value of 1. Worked perfectly.