Help With British India Half Rupee 1940 Composition

Thank you for that informative reply!
Just exactly what I needed to know.
I strive to find out as much as I can about the metal compositions because my hobby is the study of counterfeit coins.
One Half Rupee is distinctly different from the others.
For my notes, I think it reasonable to guess my piece has less copper with more nickel & zinc.
I'll see if I can buy the mentioned reference book or see if the info is available online.
Thank you so much- I just didn't know the name of a title I should be looking for.
Edited added line:
That compostion should have a SG of 9.53, and my coins do, but not the questioned coin. It is 8.8

It certainly looks good in most respects apart from perhaps porosity.
I can provide microscope pictures if any desire to see them.
Looks no different and is the same size as the others.
My idea is that it may be genuine, but struck with an improper blend of metals.
Maybe less silver or less copper but more nickel.
Just not certain.
It doesn't really "stick to a magnet" in the normal sense.
A powerful N-52 stack of magnets will almost lift it, while doing nothing to the others.
A small suspended N-52 magnet on a thread will attach itself to the coin, but not the others.
I'm thinking it just has more nickel than the others.
Not all my pages of suspect coins are straight forward and easily understood.
Some remain with uncertainties having no precise understanding.
Edit to add a note about magnets:
A number of topics concerning magnet slides can be found.
And they have their uses as long as you are careful about what they indicate. One more option I like is to have a pair of small N-52 magnets pinched together with a thread between.
Suspend the pair, approach with a test coin, and it may be surprising in some cases where the coin will attach itself even though it may not be expected.
Needless to say my population of 1940 Half Rupees will slowly descend a magnet slide while the questioned coin will not.
Just like the suspended pair of smaller magnets.
The population will not attach, but the questioned coin does.