I have a 686 6" that has the lock, which would make it a -6. Do the 686-6 models not have it stamped on the gun? Mine has the serial number on the frame (and butt) but nothing below it (i.e. 686-6). Is this common?
inside the crane - swing the cylinder out and it's in there
Unless I'm really missing something, the picture I posted shows what you are describing and there is no model number. I'm just chalking it up to being missed at the factory.