I believe it is a rupee and not a half rupee and I believe it is from India (that may be the problem, though, because I have only focused on those types). The 17.5 mm is small but it has a thickness that puts it right at 9.5 grams. I am really having trouble finding some things that I can use for identification. I am even struggling with orientation because it is somewhat unlike the standard with something that resembles "lines." I am also up in the air on what I feel are the corresponding numbers to properly date it. I have some thoughts, but nothing concrete.
I find some of the Indian Princely States coins very hard to identify. The information is very limited. Hopefully someone else can contribute some more. http://worldcoingallery.com/countries/India_all1.php
Yes, Jaunpur Sultanate. Ibrahim Shah, 1402-1440, billon tanka of 80 rati, dated AH 843 (AD 1439-1440). Goron & Goenka p. 345, J6.