I've owned my .50 Hawkin flintlock for about 7 years now. And all that time I've been using Triple 7 in the barrel with good results. Most of the time, I really haven't experienced the delayed ignition that others have when using a BP substitute with a flintlock ignition. As for Pyrodex loose powder, that's a different story (terrible in my flinter). However, today I gave Goex FFg a try in the barrel. I'm now converting to true black powder. There was a noticeable difference in the ignition time between the Goex and the Triple 7 I've used previously. Though using the Triple 7 is convenient as that's what I use in my in-line as well. The Triple 7 wasn't really a "delay" but the Goex was noticeably more "instant" in ignition.
Also, I recently started casting my own 370 grain Maxi Balls and today was my first time at the range with those. They were every bit as accurate as the Great Plains Bullets I had been using. Quite fun casting your own bullets and getting impressive accuracy
P.S. It was 0 degrees F at the range and I had the place to myself. Bright clear skies with Alaska Mt. Range in the background.