First, for some reason I left luck at 10, rather than 6 (I imagine I set target luck to 6, worrying how you can make a mistake with only 3 variables)
A head shot with just Luck 6, with better crits ...
Shooting at an Endurance 1 target should have a knockout chance of ~26.29% per shot, knockdown is additional chance of ~32.36%
Shooting at an Endurance 6 target should have a knockout chance of ~24.33% per shot, knockdown is additional chance of ~19.42%
Should read as:
A head shot with just Luck 6, with better crits ...
Shooting at an Endurance 1 target should have a knockout chance of ~21% per shot, knockdown is additional chance of ~25.23%
Shooting at an Endurance 6 target should have a knockout chance of ~15.14% per shot, knockdown is additional chance of ~18.98%
(corrected)
Second, these are head shots, so:
now for 6 luck = > (50+6*5)*60/100 % = 48% and and 6% base crit makes = 54% crit chances so
Is wrong, and should be 40/60, as 60 is for eyes, 40 is for the head. You also have to add on the bonus for ... erm, hitting? ... which leaves you at 42.5% crit chance for luck 6 head shot.