I’m going to be the ■■■■■■■ suggesting you start from scratch.
What you need is a Turn In Place system that’s properly implemented to keep the root bone in the same position until the rotation exceeds the wanted rotation.
You can follow this to get that
There is a project available for download to reverse engineer.
You’ll want to change a few things but that’s what you need to have first.
When you implement this, you are going to want to blend the AimSpace and the Idle on the Pelvis bone to get your feet and your bottom top isolated from one-another. This also solves the FootIK problem you might run into when implementing this - but there’s a lot more work to go with that.
Within the videos from the links above perhaps the most notable thing is the use of curves to drive rotation.
I’m actually using curves to drive IK as well - in case you want to add that.
Second thing, you need a proper IK system for the handling of the weapon. One of your arm bones is twisting out which either means the current IK system is not correct or that the skeleton structure in use has an extra bone allowing for that bend or not within the IK chain.
Also it’s kinda vital to have this so that you can drive the gun position for lowering and raising during aiming and have it be 100% accurate to the center of the camera always offset for the iron sight that may vary from weapon to weapon.
Otherwise it’s just going to be off and your gun will need orienting to align the iron sights - bad idea.
Probably also why the issues with the rotation you are experiencing btw.
After implementing the rotation from above, your Root Yaw is going to be directly related to the orientation of the gun, since it’s essentially center camera. You just need to solve the distance on the forward vector, offset downwards by the position of the iron sight and that’s the gun hand bone location to have it smoothly interpolate on it’s own.
For shooters, socketing the camera to the head is a bad idea unless you clean up all of your animation to have a steady head. That’s why the shooter template doesn’t use a full body mesh.
You can also follow this tutorial to kinda do the same, I think he also covers a turn in place system. Either way good pointers to go through.
All in all, creating your own animations and getting the blueprint ready can take you up to a couple of weeks even if prototyping, so I know that starting from scratch sounds rough, but if you do it right once you won’t have to live with the bugs and issues. especially if you are missing the needed IK bones or have extra bones within your current skeleton…