You may get various opinions, but in my experience:
1. 777 is MUCH cleaner burning and easier to clean up.
2. 777 CAN cause a "crud ring", a buildup of harder, crusty-feeling fouling at the point where the bullet was seated on the powder. This can be easily removed by swabbing between shots (which many do anyway), but it can make reloading a second shot in the field tougher. I believe this is made less a problem if a cooler primer is used - regardless of which kind of ignition is used. In my White Ultra Mag, it is not a problem at all.
3. 777 is approx. 15% hotter than Pyrodex. In other words, a load of 85 gr. 777 is roughly equivalent to 100 gr. Pyrodex. You will get more shots per pound with 777, if you dropped down 10-15% on your load volume.
4. Some guys say 777 has a "sharper" recoil than Pyrodex. I can't tell the difference.
There's probably more, but those are the differences I am aware of (that I can remember).
Good Luck!
