Yes, 777 is about 15% more potent than Goex Black Powder, as far as the squib loads I'm not sure but I do know that 777 does not like to be compressed too tightly just having the bullet touching the powder is better than compression I have found with my CVA Bobcat .50.
15% is what I was thinking also, but what I was seeing looked more like 50%!
As for the tight packing, I can sure see where that could happen with the range rod he made out of 3/8 brass and 46 inches long with a 3" knob. I have never used a pile driver like that before. He is making me one 36 inches.