Hi Helofxr, lets assume your meter reads 50A FSD, and that it requires 0.1V to move the neddle to FSD. Then your Shunt Resistor will be V/I=R..
or 0.1/50 = 0.002 Ohms.
This is an extremely small resistance and could be achieved by say 8 inches of 100A wire....
So don't go looking for ceramic insulated resistors that have colour codes...