The industry rule of thumb is that 3F black powder granulation can be and routinely is substituted for 2F granulation.

It's all made from the same manufacturing run at the same time...the resultant different size granulations are screened / separated out into different hoppers as their different sizes result in different burn rates, therefore different pressure curves.

Just reduce whatever the 2F load data is by 10-15% to keep the pressures in the same range...ie: if a load calls for 100grns 2F, just use 85-90grns 3F instead.