I feel 30grns is max in BP and Pyro (reduce by 17% for 777) pyro and BP should be identical measure for measure.
12 to 15 is a bit light for a novice, when your loading technique is more practiced you might find a lighter load better. As slowcoach suggests around 20 should give good results.
“If a cricketer, for instance, suddenly decided to go into a school and batter a lot of people to death with a cricket bat, which he could do very easily, I mean, are you going to ban cricket bats?” :- Prince Philip said after Dunblane