There are disadvantages to everything, and H777 is no exception (life's a compromise). It's fairly difficult to ignite. It will not work in a flintlock gun without a small charge of black powder beneath the H777 charge, and the priming charge (in the pan) must also be black powder. I've tried it, and decided that the presence of black powder residue negates the cleaning advantage of the H777. So, I use pure black powder in my flintlock guns.

Although I don't hunt in extremely cold climates, I can imagine that H777 might be hard to ignite in a percussion gun at sub-zero temperatures (but I don't know). This could probably be overcome with so called "magnum" percussion caps, or switching the gun over to musket caps. Again, this is conjecture.