diito re gyraf regarding moving iron meters. You can usually tell from the outside about those: the vane/needle is just emerging from a semicircular slot in the faceplate. I think one brand of this type was called Readrite, which of course prmpted people to call them Readwrongs. The field generated by the current is pushing the magnet on the vane against a spring.
There is no modification to this type of meter, to speak of, that will give it milliampere sensitivity.
Decent high-sensitivity meters will have a more complex motor usually visible to some extent from the front. The D'Arsnoval movements have little rectangular coils with very fine wire and some mechanical bearings, sometimes jeweled. Another type is the taut-band variety which looks a bit different.
If you rock/rotate the meter and the needle doesn't move much, it's probably not a high-sensitivity movement inside. However, if there is a low Z current shunt inside this will tend to damp the needle motion quite a bit, but still it will be more responsive than a moving-iron one.
Brad