Careful with pressure
Please be careful to note the difference between 777 and Pyrodex, pressure-wise, it is 15%. I have a gun in which I normally use 80 gr. Pyrodex to shoot 1-inch groups at 100 yards. I use 70 gr. 777 behind a 180 gr. bullet (this is for does, deers, female deers, at close range).
Using 150 gr. of 777 in a 150 gr.-rated gun probably won't make it blow up because of the extra insurance factor added to the rating but still, be careful, as the pressure difference can affect your accuracy.