FYI,
There was never a Factory built Steyr Aug W/ a factory 24" Barrel, they either came with a 16" or a 20" Barrel only, the 24" Barrel was an extra accessory, it was used on a Steyr special receiver and or as an accessory to a factory 16" or 20", if you do find it, the numbers will not match, thus it is not a factory built unit.