On Wednesday, January 2, 2013 9:15:09 PM UTC, The Natural Philosopher wrote:
On 02/01/13 19:53, wrote:

Stable R metals like constantan wire have too much R for this.

Not if they are solid bars, which many ammeter shunts are.

obviously, I was addressing the idea of using wire as a homemade shunt

Low resistance metals like copper change R as they heat up.
A simple diy solution when making a shunt from something like copper is
to dip it in water, then temp changes are far smaller.
In principle you could probably also use a cup-like shape.