I think rotating the gun is definetly a great idea. I think I would consider giving it a try to make the gun rotation more "freely". Maybe press a button and then instead of "looking" with the mouse you are now rotating the gun freely in your hand. I have no idea if this works but I would be really curious. It would be controlled similar to the Hand simulator game (https://store.steampowered.com/app/657200/Hand_Simulator/)
) which does not take itself too serious and is really clunky but loads of fun for a short time.
I hope you understand what I am going for here :)