The squib loads are very likely to have been caused by overcompressing the 777. I use a 38" solid brass range rod to load and have to be careful not to compress 777 too much with the rod. I usually clean every third shot when using 777 just to be sure I have a clean enough bore to be in control of the rod when loading. I ease the ball down the barrel until the rod stops, check the rod mark to see it's fully inserted, and then give it just a light extra push with just one hand.
As far as your chrono data, your 777 numbers seem too high to me. You might check them with Hodgdon's web site. I don't see 50% hotter in your numbers, but they are higher than one would expect. Are those numbers averages, and if so, what were the spreads like?