Well it *was* a 770. I just upgraded to a 1025R FILB w/MMM
Still have the bit, but haven't tried it on the 1025 yet, I've only had the 9" auger on that so far.
(but I've only had the 1025 for 15 days).
Luckily for the 770, deck footings only had to go down 12 inches (or maybe it was 18).
The only one that hit a significant rock, I just relocated the post.