This was just a bad assumption on your part based on how you wanted it to work.
Just because the barrel is one object does not mean that within the engine you can only have one object.
You make a blueprint that detects the presence of a nearby player (probably on hit) which allows you to push the barrel by simulating physics.
You then turn the option off/stop simulating so you can shoot at it without causing it to move.
You can then swap the barrel for a skeletal mesh to play an explosion animation, for instance.
You can even just have multiple blueprints so long as you tween and polish how they swap out one another.
Eons late by now, but maybe it helps the next person around…