She's currently an illegal design...
AC/5 didn't debut until after she was created, making her illegal per IO design date.
Now as for a possible retcon, the Heavy Rifle was around, same weight, one less crit but only 9 salvo shots per ton... So we need to drop two tons from cargo to get the necessary 10 shot minimum needed, 18 total per gun.
And further note, the AC/5 could be the upgraded navalized variant of the MoC that's talked about.
TT