Rifle, thanks for the thoughts. Important stuff, that.
I was concerned that "wreck" might be interpreted by some as "explode", as in catastrophically destroy the cylinder, the classic result of using smokeless powder in a bp revolver. I'm not aware of that ever happening as a result of using 777 in any amount or granulation.
I've been using 3f 777 almost exclusively for about 2 years and have seen no damage to any of my Colts, especially a Uberti 2nd Model Dragoon. I load for accuracy, which pretty much limits my loads to between 20 and 25 gr of 3f 777, depending on the gun. The Dragoon a bit more, usually 30, but never more than 33, and an 1862 Colt Police uses 17. Well, I did use 40 in the Dragoon once, just FTHOI, and I won't ever do it again. I have no idea where the rounds went as accuracy was not-existent.
There is no question 777 is hotter than regular bp, and the rule of thumb of 15% seems about right to me. There is also a good body of chrono evidence to support that figure. As for 2f vs 3f, I'd suggest that, if one wants or needs to use 777, then he or she should use the same granulation that one would use in black powder, but 15% less. Thus for a load equivalent to 30 gr FFg black powder one should use no more than 26 gr FFg 777, and for 30 gr FFFg black powder, 26 gr FFFg 777.
If it became necessary to use a different granulation then be guided by what you would do in switching granulations of black powder first, then factor in the 15%. FFg can be used in place of FFFg as it burns slightly slower and produces a little bit less peak pressure, so I'd suggest using a 15% reduced load of FFg 777, if necessary. However, going the other way, using FFFg black powder in place of FFg black powder, some folks like to reduce the load a bit, say 30 gr down to 28 gr. in that case one should reduce by 15% X 28 gr = 4 gr, to 24 gr FFFg 777.
I use 777 for two reasons: it's easier to clean and it's much easier to obtain. I have recently found a good nearby (50 miles one way) source for retail Goex black powder, however, and will be using it more often in the next year - I do prefer how it smokes and smells. But 777 is a fine product and although Goex is now more readily available to me I won't abandon it altogether; it will remain my standard for evaluating performance of my bp guns.