An Etymological Dictionary of the German Language/Geschoß
Geschoß, n., ‘shot, missile, dart,’ even MidHG. geschoȥ, OHG. giscoȥ, n., akin to schießen. So too Geschütz, ‘artillery, ordnance,’ even in MidHG. geschütze, n., ‘arms, weapons for shooting,’ occurs as a collective of Geschoß.