Third person line traces are a bit complicated, but it generally requires at least two different line traces depending on what you are doing. A simple weapon firing system is something like:
One from the center of the screen forward to a fix point in space or until it hits something and then another starting from the characters weapon muzzle and ending to the point in space from the first line trace or whatever hit location it has referenced. Given that your screen is moving with camera shake to emulate weapon sway you should still be safe to approach it this way.
There are other posts on this forum with screenshots already posted that should get you started, but unfortunately I’m not able to point you directly to them at the moment.