The first thing to know is whether or not you ammeter reads current directly or does it read mV and thus need a shunt.
Shunts normally put out only 50 mV at full current and are rated in terms of output (50mV or 100 usually 50) AND for current in circuit 5 50 500 etc etc.
You can get good instrument rated designed shunts from any good industrial instrumentation outfit (in Seattle Branom inst). Yes you will pay around 25 but it will almost never burn out.
Dan Bentler
