Depending on what rifle you have.. that would answer that question. Some of the rifles allow 120 grains of loose as a max load in 2f. Some such as the BPI barrels and older inlines I think had a 100 grain max load limit.Again in 2f grade. When youincrease to the 3f grade you increase the barrel pressures. The usual number thrown around is 15% decrease in charge strength when changing from the 2f to 3f.

Also the length of your barrel will make a big difference. If your shooting a 22" barrel there is no need to shoot over 120 grains of anything because you are wasteing it. If the barrel I believe is 28" it will manage to burn off 150 grains of powder.

So to answer you question I will say NO! it is not save to shoot 150 grains of loose American Pioneer Powder especially the FFFg grade. I would keep the loose powder 3f charge around 100-120 MAX. In 2f and pellet form the go ahead and shoot 150 grains. If your rifle allows such loads.

Do not be surprised if your accuracy flys out the window as fast as your money, shooting those large charges of powder. Especially when shooting pellets.

What kind of rifle are you shooting? I do not remember reading it in the posts... Good luck with your rifle.