Your drop weapon needs to have a replicated inventory. I use a struct in mine do to all the attachments. grip, optics, cosmetics, mag type, ammo, muzzle, stock, canted sights etc.
When I drop it I copy the struct to the simple world pickup item. Just need to remember to check the weapons inventory on pickup and configure the one you spawn and attached.
Ammo reduction and reload has to go through the weapon class inventory as well.