Making a fake arm for a character

Hi, I am trying to make a game where the player has a custom metal arm. Everything mostly works, however there is a problem where the arm messes with the player’s movement and rotation. Currently, I have just created a separate part, made it non-collidable and massless and welded it to the player’s right arm. However when I want to turn in third person, the turning looks jittery, as though the fake arm is still rotating the model. I have tried to show it in the gif below, but it’s hard to showcase the problem without seeing it yourself.

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I initially tried to fix this with an AlignOrientation, however this ends up locking my character’s overall rotation, which I do not want. I have also tried to just rig the fake arm to replace the right arm but the rotation of the joint was the wrong way and the arm itself had a different mass compared to the left arm, which had me slightly worried that it would be imbalanced.

If anyone knows how to solve this issue, please reply.
Thanks.

Alright, I have tried to temporarily replace the rig with a default R6 rig and it also has that jittering effect. I then tried to use an R6 rig as the startercharacter in a new place and there is no jittering. This means that there is probably something in the game that causes this.

I’ve done that already. I have also figured out that it’s not the rig that’s causing the jittering, as shown in my first reply. I am currently in the process of finding out what’s causing it, I’ll probably just close this topic since it’s basically solved though.