A turret displaces 1dT and holds three missiles plus two reloads (Traveller Book 2, Space Combat, Ordnance Launch). The missiles are considered to be 50kg homing missiles (Traveller Book 2, Design and Construction, Weaponry). Even accounting for space for a gunner, that leaves quite a bit of room for stuff other than three 50kg missiles and their reload assembly.
I've no idea what all that extra space is for, but for whatever reason, there is a decided limit to the number of missiles that can be launched - one per launcher, with no more than 3 launchers in a 1dT turret - even though there appears to be no limit to the number of missiles in flight at any given time. Why, I don't know - Traveller rules very often give more weight to play balance than to technological possibilities.