Inventory/Weapon Items Set up. Best practice/idea?

So Im having another shot at it. But cant seem to see how I can fix it.

Basically because I am casting ItemBP as a WeaponBP to access the Weapon Details which are a part of the ItemBP Child Class WeaponBP. If I can find a way to access WeaponDetails(its a structure) from the ItemBP level without having to cast the object then I can easily go on with my inventory system.

The reason I want to do this is because each inventory slot needs to be able to hold any of the children of the ItemBP class(Weapon, Consumables and Key Items) not specific slots for weapons etc. Because Inventory juggling is a keypart of the design exactly like RE.