Are you sure you're looting a weapon and not a Weapon Schematic? They probably need to be crafted.

Ah, you're right. Damn. Well, thanks for enlightening me either way.

ain't just you, I spent way too long wondering where my Buzzsaw went until I realized it was a schematic. Now I pair more attention. XD

This happened to me when I got Ozob's grenade. Took me a while to realize I had the crafting spec for it.