How Do I Rotate Something Without Lag?

Hello, If you are familiar with any FPS games, then you will understand what I am saying. I am trying to make arms that rotate in accordance with where the camera is rotated, and I am trying to find a way to do it without lag. I have tried Object and World vectors, but those can be very laggy. I don't think it is possible with body velocity and body gyro, but I have played games that have almost no lag and the arms move perfectly. How can I do this? How can I create the arms, and how can I constantly rotate a part without lag? Thanks for reading.