At risk of taking this way too far...
GK (above decks) 7.9 tonnes
GK (below decks) 3.7 te
Exc ammo = 10.9te
Phalanx 1B inc RCS, LCP, ex Ammo = 6.97te
So nearly 8 te difference (ex ammo) for a shipset and as posted elsewhere, GK needs a below decks bulk loader....
Now then - who wants to guess why a fair bit of the superstructure is well known material about three times less dense than steel.......