I am currently in Siena Italy and at the villa I am staying at, I found a US Army button from WWII in the ground and I also found a bullet casing but it is not American. The bullet has P28 So Ex?39 engraved on it. The question mark is a letter or number that I cannot figure out what it says. Can anyone help me identify the era of the bullet casing as well as what country and weapon it came from???