I have a pre-existing #6-3 cable (without ground) with metal cladding on a 50-A two-pole circuit that was wired into a range. As shown in the photo, this cable has only black, red, and white conductors, plus a thin bonding wire.
I am replacing the range, and would like to provide a 4-wire connection, including ground (I'm aware that the 3-wire connection is legal, but the grounded option seems far safer to me).
Can I use the metal cable shield as the ground, even though it won't be nearly as conductive as a separate #6 (or at least #10) ground wire? If so, would I do that simply by making sure that the metal shield and bonding wire are securely attached to the metal box where the receptacle is installed? For easy installation of the 14-50R, I am hoping to use this product, which has a metal back with punchouts.
If not, what is the simplest way to safely install the range? Can I run a #10 ground from the subpanel along the outside of the existing BX? Or would I need to replace the breaker with a GFCI in order to achieve the appropriate protection?