Hi, there's a model flag parameter which forces the model to use hitboxes as collision instead of its bounding box. There are three ways to set that flag.
The first is editing the model's .qc file, you would just have to add the line "$flags 512" (without quotes) and compile the model.
The second is to open the model in Paranoia Model Viewer version 1.30, go to the tab "Misc", enable the checkbox "Hitbox collision" and save the file.
And the third one is to edit the model's binary with the "HxD" software, for more information on this method see this
Setting that flag, you will have the collision rotating with the model.
For more info on goldsrc models, see this