I did a LOT of testing with both grades of 777 and what I found is that you really don't HAVE to reduce your loads when going to 3fg 777. If you look at Hodgdon's load data, you'll notice that there is only about 50fps difference between 2fg & 3fg 777 loads for identical bullets - a difference that really makes no difference.
In field testing with my Knight USAK, identical loads of each powder gave me identical points of impact. I DID find that I got better accuracy (tighter groups) if I used 2fg on sabot bullets 300gr and less, while sabot bullets heavier than 300gr liked the 3fg cut better. However, both Conicals and PowerBelts worked best with the 2fg cut no matter how heavy the bullet was.
Not dropping the 3fg load with 777 should not be applied when using true Black powder or Pyrodex. In those powders, the 3fg cut WILL need to be reduced for safety & accuracy.
I believe this difference is due to the fact that 2fg 777 is already cut SO fine, that there is very little difference between the 2 777 cuts. This probably also explains why 2fg 777 is about 15% more powerful than 2fg Black or Pyro................ it's as much the granulation as it is the formula. This also probably explains why the new Black Mag3 powder is more powerful too and can be used in rifles or pistols - it's a cut equivalent to 3fg.