I'm currently using the FPS Shooter Aiming package, I hope it's okay to post it here even tough it's one of the free ones.
Since i'm working on a multiplayer game, I can't parent the guns underneath the player right hand, as that would require making the hand, every all of it's parents in the hierachy network objects.
So the way i worked around that was to have the gun "parented" by a multi-parent constraint.
However, the asset does not work with this approach.
I'm sending two videos showing it properly working when parented directly to the hand and what happends when it's not.