Don't mix em. I know from personal experience, I was at the range and loaded my last loose 70 grains of Pyrodex and usually go to 100, well I had brought a new power (777) and figured 30 grains shouldn't hurt so I topped it off. All of this was done in my first week of muzzleloading many years ago when my head was only on women and being invincible. Well I loaded the cap and got all seated and pulled the trigger and pow and pow. There were two explosions and from what I could tell, the initial cap firing did ingnite the Pyro and then the 777 which burns hotter than Pyrodex. I had to rethink what in the hell happened and examined the Pyrodex container which had a little moisture in it. I guess there was a delay in the initial explosion and when it did ignite, the 777 was also ignited almost at the same time as the Pyrodex as there was two pows. Looking back it was stupid, but the bullet mysteriously hit the bull at 100 yds. Just one heck of problem. As Cayugad said there is no way to get consistent results and the other hazard is, some of the new powders have such high pressures that mixing will result in dangers that you can only imagine. Just don't do it.