Cereal Mash

[SHIELDS EXILE]

I am making a small brew of Broughtons old Jock,7.5 litres. I mashed700 gms of pale malt with 300 gms of corn meal ,which is very cheap grain 1 dollar per kg.,and35gms of roast barley .cereal mash at67degrees C for25 minutes then boil for half an hour, cool to66C, added afuther 300gms of pale malt and main mashed for 90 minutes in picnic cooler. redult5lires at 1064 plus 4.5 L sparge liquer at 1018 This gives 320+90=410 points from 1.33kg of grain=308 points or degrees of gravity per kg. this is over 100 per cent efficiency., or are my calculations wrong.