Using SE 3 conductor SE cable for 50 amp stove wiring. Cable labeled 3 conductor 6 AWG. Two insulated hot conductors and uninsulated bare wire. Is it permissible to use bare conductor as neutral. Installation instructions permit wiring as 3 wire or 4 wire.

The uninsulated conductor in the SEU cable you describe IS a neutral, but...
This is not legal for a new range circuit. Hasn't been for several code cycles now.
You must use SER cable with three insulated conductors and a bare ground.

Not a new circuit, just a new stove. Don't want to pull new cable unless I have to.

Oh, for existing circuit you are still fine.

Thanks Stan. That was what I thought but I wanted to be sure. I know what I don't know. I wanted to be sure so I ask you.