The trick is to make the shunt steel, not copper. It has enough higher resistance that a small amount of the current still takes the path of least resistance- - -through the ammeter. This causes the needle to deflect. The shunt simply allows enough of the current to bypass the ammeter that the needle doesn't peg out in high-current situations.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!