I’ll get back to you on your Q after the game-jam.
For now, suffice to say that you can dig into the IK Content example on your own along with the IK training videoshttps://youtube.com/watch?v=vZW8mxlQJEk
That’s the base from which you start.
As you will see (or already saw) the hands have a Root bone.
What you want to do then is link a socket placed on the Front Sight, one place on the Rear sight (so you can line them up and get a picture perfect sight), and shift the weapon up enough to get those 2 sockets to have the same Z as center camera (with a scalar for adjustment so that different sights can be offset easily).