Why does the SRM6 suffer a short fall in shots per ton? I am sure it has been asked before but I never heard the answer.

It seems LRM's are divided by flight lots out of 120 and SRM's out of 100. All the LRM flights math works out to 120 exactly. Is there a reason SRM 6 Ammo is heavier than SRM2 or 4. Because simple math says there should be 16 shots per ton. 16x6=96

LRM 5 24

LRM 10 12

LRM 15 8

LRM 20 6

SRM 2 50

SRM 4 25

SRM 6 15