777 is a sulphur less mixture so you don't have that NASTY rotten egg smell while shootin, or more importantly, while cleaning up in the kitchen!
It is true about the 777powder being more powerful than a volumetrically exact amount of Pyro. 777 pellets aren't actually 50 grains, they are volumetric equivalent too 50grains of Pyro. If you weighout 150grains of 777 powder and set it off in your gun, you WILL get your eyes crossed...
Good stuff tho and I never had a problem with cleanup when I was shootin it!
RA