Floating Skeletal mesh

I’m making a mod in Robo Recall, and for the life of me i can’t figure this out.

I have just followed the tutorials with everything, and have my own mod shotgun, and I just wanted to swap out the mesh for one that I converted from an .stl file. Everything seems to work, and I eventually figured out i needed to make a skeleton and set it up as a skeletal mesh with a physics asset.

But when I get in game this happens:

They just float there!
I have tested and they do have collisions for me throwing a cup at it, and hitting a robot with it, and shooting it; but it just does not fall to the floor.

Can anyone help me figure this out?