There is a bit of a fluff disconnect, in that rules wise an a ton of srm's is a ton of SRM's and useable in any SRM launcher, with the only tracking needed being for specialty types (streak, inferno, etc) vs standard, and iirc clan vs IS (and that easily converted between) ditto for LRMs and so on.
While the fluff suggests that different brands use different sizes of missile and such.
The same goes for autocannons.. rules wise an ac5 is an ac5, but fluff wise it might be anywhere from 30mm to 120mm bore.
Generally for gameplay purposes you want to ignore the fluff bits, since they just complicate campaign logistics tracking. Same reason why repairing armor and actuators and such is just a cost, with no parts tracking.
If doing an rpg game though it is up to the GM how detailed they want to get.