So, if I understand you correctly, what are you suggesting is like box launcher, but instead of one missile there will be internal magazine which this "pod launcher" reloads from...
What's the point of it? This kind of launcher will either almost completely replace conventional launchers (if it is better than them), or not get used at all (if it is worse than them), because this IS conventional launcher, only with internal magazine instead of external.
The bonus from "missile launcher turret" looks wrong, because to-hit chance is determined not by FC, not by launcher, but by missile itself.
Also, your suggested formula for size gives result which is even less than size of missiles themselves. (30*0.15 = 4.5 HS versus 3.7 HS).
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Well, this idea could work, but in slightly another way.
For example:
Not reduced size, but FULL size of launcher.
Better firing rate than conventional launchers, but not the 1/ReloadRate; its too fast. Maybe 0.5x reload time?
Reloading from hangar\maint facilities only; reload rate is 60s*<total mass of missiles IN MSP>, so for example, 30 missiles of size 3 will take 90 minutes to get reloaded. Missiles are reloaded one by one OUTSIDE the ship, but INSIDE hangar\maint facility, so interrupting reload will just leave the magazines empty, and missiles are added to the ship which was performing reloads or, if there's no space for them, simply dropped out into space.
Missiles are stored inside internal magazine with fixed\researchable efficiency, but not more than 80% (20% of mass required for internal reloading system to keep firing rate).
And formula for mass is:
(<amount of missiles>*<size of missile in HS>)/<magazine efficiency>+<launcher size>
Example for 30 sz3 missiles:
(30*0.15)/0.8+3=8.625 HS
This is only an example, but in this way either pod launchers and conventional launchers will have their own purpose.
Pod launchers give an ability to quickly unload large amount of missiles at the cost of less missiles per ship compared to conventional launchers.
Conventional launchers stay the same.