Can't loot Rivet Gun from first Rosie in BioShock Remastered

Solution 1:

Wiki says:

Because of its massive size and weight, the Rivet Gun cannot be wielded by a human such as Jack.


Perhaps you looted it already and just didn't notice? Or do you have to unlock U-Invents before you can loot it, since its primary items are crafting components?

Wiki says:

Starting with Arcadia, the player begins finding various new items when looting and searching, as well as finding the first U-Invent machine for using these items.

I assume the phenomenon you experienced is what it's trying to say. "Certain new container types and loot are unlocked."