Which has more velocity Black Powder or 777.
Generally 777 loose powder is 15% to 20% more efficient than Black Powder. But the Standard 777 Pellets (nto 777 Magnum Pellets) were designed to be the equivelant to Black for obvious safety reasons.
85 grains 777 FFG by VOLUME is roughly the equivelant of 100 grains of Black Powder by VOLUME.
80 grains 777 FFFG by VOLUME is roughly the equivelant of 100 grains of Black Powder by VOLUME.
Two 50 grain 777 Pellets is the equivelant of 100 grains of Black Powder by VOLUME.
Most magnum rifles capable of handling a 150 grain volume charge of black powder can also handle three Standard (not Magnum) 50 grain pellets of 777, but only recommend 120 grains of 777 loose powder.
So three 50 grain 777 Pellets (150 grain charge) are the rough equivelant of 127 grains of 777 FFG loose powder by VOLUME or 120 grains of 777 FFFG loose powder by VOLUME.
The new 777 MAGNUM Pellets would be the 777 loose powder equivelant, so two 777 MAGNUM Pellets would be the equivelant of 120 grains of 777 loose powder, which being 15% to 20% more efficient would also be the equivelant of 150 grains of Black Powder by VOLUME.
The newer BP Substitutes can be very confusing, so it is better to find out here than on the range.
I hope that answered your question without confusing the heck out of you.
The simple answer to your question "Which has more velocity Black Powder or 777." would be 777 (by 15% to 20%) on a equal VOLUME basis for loose powder, but with STANDARD 777 pellets they would be equal to loose Black Powder equivelants (one STANDARD 50 grain 777 pellet = 50 grains loose Black Powder). Also see MAGNUM 777 Pellet equivelant above.