How to animate arms in realtime

So I've been trying to make a character that has controllable hands, but I just can't figure out the right way to do it. The idea is to have a first person character with a gun, bow or practically any other weapon and when you hold right click you could move the gun around in your view so you could manually aim. The problem are the elbows and shoulders. I have no idea how to make them behave naturally. I'm using a blender model with a rig. I figured that it can't be done via animating in blender because i want to be able to literally have the ability to move the players hands freely, not into certain positions. scripting seems to be the only way but before I make a giant script for this, I would ask the community if there is any good option. Something like bones in unity or anything that could make the arms behave like human arms not rubber arms.