Pyro is the evilist of concoctions. It is a modified BP rather than a subtitute. It was developed to be "non explosive" to get around postal (DOT)and storage (NFPA) restrictions in th US.
777 is a modern substitute it contains no sulfur so residues are very much kinder of your gun. Ruducing the long term damage to my piece is more important to me than authenticity. It still smokes and goes bang so it looks right, I just dont go home smelling like rotten eggs.
“If a cricketer, for instance, suddenly decided to go into a school and batter a lot of people to death with a cricket bat, which he could do very easily, I mean, are you going to ban cricket bats?” :- Prince Philip said after Dunblane