There seems to be some major issues relating to replication with your plugin (Currently testing in 4.22). I thought it was bad logic, but then I tried my logic with BallisticsFX and it worked just fine.
Since the plugin hasn’t been updated properly (only doing UE4 release updates), there’s a chance that the original replication logic does not work properly anymore.
Also, while Barrels look to be a SceneComponent sub-class, they cannot contain visual data like a regular Actor would, making this very cumbersome to use. I currently have to put the Barrel and my Visual Element (static mesh) into a regular Actor BP so I can organize my logic better (then putting them into childactors in the vehicle BP)
What you could do instead is subclass it under StaticMeshComponent and SkeletalMeshComponent (so two different types) BarrelStaticMeshComponent and BarrelSkeletalMeshComponent. Same goes for the Bullet actually.
You can see code examples in the VR Expansion Plugin https://bitbucket.org/mordentral/vre…in/src/Master/
I have tried to reach you over the past few days to no avail (even though it has shown you online).