After much checking though I am fairly certain this is actually a
Vietnamese coin - Thien Hung Thong Bao.
While it is hard to make out the second (6 o'clock position) character, none of the many
Chinese Tien
XXX Tong Bao options appears to fit.
These coins were originally
cast by the
Vietnamese rebel prince Lang-son Vuong in 1459-1460. It is known as
Toda #163 from an old
Japanese cataloger.
However, this
type was subsequently copied throughout the region. Yours appears to be a privately minted coin from the
style and condition of the casting. Possibly a Javanese imitation.
SC