One wonders who's hands last held this thing when it was "alive and firing". Some young Hitler Youth firing at a Soviet T-34? Or some grey haired old crippled man leaning over a pile of brick rubble? And did the shooter succeed and lived to get away after taking his pot shot? Like they said, it's unknown history must be fascinating but forever lost. It did clean up pretty decent!
(I always soak stuff in White Vinegar, myself-it's slower, but relatively safe!)