I'm changing 2 prong outlets to 3 prong. The house was built in 1957. The boxes are grounded as there is the bare wire coming into the box and wraping around the screw in the back.
Whats the best way to ground the new receptables? a self grounding receptable or a wire from the green screw on the receptable to the screw in the back of the box (where the grounding is attached)?
As long as the ground wire is attached to the box, the box is metal, the mounting screws go directly to the box, the metal of the receptacle will touch the box when screwed tight ,then you should be good. If there is a gap and you have to shim the receptacle, then you will need additional ground conection. There are specification grade receptacles which have a ground spring at the mounting screw. You can also use the ground jumper to the back of the box, but only one wire on the screw, so you may have to pigtail.