you can use event dispatcher “Ready to shoot” to rotate the EbBarrel to a specific rotation. if you are looking for a rotation of your crosshair, just line trace from camera center forward, get hit impact point, and use the function “find look at rotation” from the barrel component to this point. set world rotation of the barrel. and there you have it.
https://www.youtube.com/watch?v=h-CtH748XN0&ab_channel=AngeIV
Example. 
This is made with single mesh FPP view, ik aim offset and easy ballistics.