Back and Forth Rigging Motion Help from 3ds Max

I am having trouble getting a rigged object into ue4

i am trying to create motions with bones in 3ds max that are straight back and forth motions like a pump action shotgun handle.

i made three bones, one to weight the mesh to and the others to drive back and forth motions on other parts of the mesh.

problem is if i link them together in max the bones rotate instead of going back and forth and Unreal Engine says i have multiple root bones if i export them unlinked together.

I have searched the net for an answer but i cant find one -_-*