Welcome to the Forums here..
I use 100 grains (2 - 50 grain pellets) behind a 250 grain XTP.
A nice Buck agreed this past season that it is a lethal combination.
In mine, loose 777 opens the group up slightly. Pellets seem more accurate.
But I do not weigh my loose charges, I use a volume measure.
If I weighed the charges it would probably tighten the groups back up.