I did some playing around with the spreadsheet trying all sorts of variations on the shank and so on. It really did not amount to much difference.

However, I am not going to change the specs and I will leave it a .860 muzzle diaemeter and 32 inches long. This will make sure I make weight with a bit to spare and it will give me some peace of mind. Plus I can always attach a cappucino machine or a windmeter and still make weight.