Bought this at a recent estate sale. Family history had it being brought back from New Guinea by Grandad after WW2. Pretty sure it’s not a US Military shell, but I really don’t know. 9 inches (228mm) tall. 2 15/16 inches (75mm) diameter at base.
I am making a WAG that it is a Maxim-Nordenfelt 14 pdr… I’m sure someone will provide the definitive answer shortly.