You should try just setting the discs transform when it is spawned to be what you want… then the projectile will fire in that location, rotation and scale. A projectile only gets “shot” once and travels along its x-axis. I would split the pins on the transform and the rotation and do the randomness thing there. The objects velocity will be handled by the physics engine based on its initial speed setting.
The static mesh I have here moves and rotates in world space but the projectile always spawns from in front of it. You should be able to apply the same principle to what you are trying to do.
Your probably not going to do anything physics related to the reference to your freshly spawned actor… let physics handle that. If you want to alter the arc you should change the discs mass or the initial speed. Of course you will want to apply the math for the randomness to the rotation not the location.