Still haven’t figured out why the gun magicly snaps into the hands with the Arms Mesh provided and not other arms meshes I use. The skeleton and animations are the same.
Edit: Nevermind I figured it out on my own lol. The problem was the mannequin arms didn’t really have the weapon_mount bone on it. Added a video on how to add this bone in blender for anyone that may have the same issue.
( ignore my raspy voice and the sniffles, I got a cold 
)