"So, to accelerate 1.2 million lbs by 6 gees, sea level must be pushed down by 12,566 cubic ft times 6.
Which is 77396 cubic ft, which is pushing the water down 60 more feet.
So as long as the water is pushed down 70' under the sea level the pipelaucher will accelerate at 6 gees. So 70' requires 31.2 psi of air pressure."

Oops, stupid mistake.
Instead it needs 18727 cubic feet of sea water, so times this by 6 which is 112,362 cubic ft, which pushes water down 89.4' and then add the 10' which gives 99.4' which is 44.3 psi of air pressure.

Anyway, replace any mention of 70' with 99.4' and 31.2 psi with 44.3 psi.
And that makes 1.2 million payload at 6 gees not possible- at least not safe and having any safety margin.
So, somewhere around 1 million lbs of payload is the max with 6 gees with this design.

2.2 million divide by 64.08 lbs is 34332 cubic meters.
And divide that by 1256.6 sq ft is 27.3'.
Times 6 equals 164'. Which is 73 psi.
So 1 million lb payload at 6 gees for 2 seconds is about
as much as this thing could do.