How to bring reticles in different situations to the center of the camera?

I'm making a part to look into the optical sight and scope when aiming in an FPS game now. The gun is a child object of the right hand when it is not aimed, but when it is aimed, it has a parent-child relationship of "MainCamera> gun body". This creates a state where the gun & scope is always in front of you no matter which direction the camera is facing. The problem is the alignment of the camera and the reticle. Of course, the sight reticle must fit in the center of the camera. However, the position of the reticle differs depending on the optical sight and scope, and since it is a child object of the rifle, it is also affected by the height of the rifle. Is there a way to always bring different reticle of different firearms to the center of the camera, as the only thing that can be moved freely is the rifle of the parent object?