I have only a faint memory of hangfires since I used the last of my Pyrodex about 17 years ago. The stuff drove me nuts. I found it only worked for me in an "in-line" ignition system. By that I mean a cap-n-ball revolver - not the other, newer in-lines about which I know nothing. At the time I though maybe it would reduce some of the gooey-ness associated with shooting those pistols.
Seems that Pyro flash has a hard time turning corners. With BP there is never a doubt. I've used it exclusively for some 20 years now in my Tennessee Mountain Rifle and my GPR .50. I have never had a hangfire with BP in those guns - no matter the weather.
I shot muzzleloaders for 12 years before I ever touched a cartridge gun. I just didn't have the interest because I was having so much success with BP - especially during those special seasons. For those interested, here is my "method" for eliminating the chance of hangfire.
1. When you get your rifle, make sure that the hammer cup strikes as square as possible onto the nipple. They don't always line up and a "half-moon" strike pattern on the hammer cup will certainly tell you. More importantly, look to see that the hammer is aligned with the nipple. It should strike full on and not hit the side of the cup first. Use dry BP only.
2. As a religion, swab your bore with more than a dry patch before shooting. Actually, clean it to remove your storage lube. Then dry swab to dry. Make sure you remove that cleanout screw at the nipple bolster (on the GPR type) and treat that bolster like the barrel. Dry it. On a removeable bolster like the Tennessee, remove it and do the same. Use dry BP only.
3. Now, pop at least three caps before loading - use more caps if the sound is not uniform and the pressure form the muzzle does not move a blade of grass. Caps are cheaper than dirt so replace them every year. Yes, I have used some very old caps that worked fine but that was a long time ago and I just don't do that anymore. Use dry BP only.
Now, if your flash channel does not have a large tooling burr somewhere that is blocking, and the breech threads are not too far into the chamber, it will go off. It simply has to. And, did I say to use dry Black Powder only?