How can I keep my weapon correctly in my hand?

Well thats what i have setup right now, however some of my models don’t work well, like some of my skeletal meshes are perfectly in the hand and my other models are all unplaced and not working, The only thing i found that actually does sometihng is if i export each individual model into an editor, change the position, and keep re-importing into the characters hands. This absolutely awful though, half the time it looks jittery and its very time consuming, as well as when you aimdown sites its terrible. What do i do?