This is an old thread, but I stumpled upon this too. What I found as solution is, you should not set ReplicatingMovement to true and not use PostReceiveNetUpdate (The comments of the interpolation parameters can be read that you should use them).
Instead make you own Location and Rotation replicated properties and in OnRep of these you can call the MoveInterpolationTarget() function, then it should work.
But still, the projectiles are glitching around a bit, not choppy, but they teleport to a complete off location for a frame sometimes. I think I will override the interpolation method to use a simple interpolation on my own.