I'm sorry I just read what you said and I'm lost your breeding 288 rats and only 6 on average are giving birth???
Now all of this is on average
You said
I use a standard 6 tub rack
I run 1.4 per bin
I figure 10/ litter

SO by my calculations I quote, I can produce roughly 240 babies per month(60/week) per rack.
So at an average of 10 a littler thats 6 moms on average a weeks giving birth.

But you said that
I currently have 72 tubs of rats and plan to expand another 84 tubs.
72 tubs with 0.4 in it is 288 females with no resting in between breeding and your not separating them you only getting, per month on average 24 females a month...so your birth rate is 8.33% success rate?? on average??

Or is this for a smaller group than the whole collection??