Thanks, all. The John Manton is advertised, way back then, as a self primer. When the powder is tamped down, a bit is supposed to leak out into the pan. My 16 ga. gun was loaded with 3fg as it seemed fine enough to self prime. The first shot detonated properly without added priming. The other barrel did not detonate. I primed the unsuccessful barrel, but still no detonation. I discovered that the unsuccessful barrel's flint was a bit loose. After repositioning and tightening the flint, it fired properly. Lots of slow, delicate preparation in operating a flintlock. No wonder that the percussion gun, and then the pinfire became more popular.
You got some good advice on powder granulations. In spite of the self priming feature of the Manton lock, I think I'd still prefer 4F for priming and 2F in the fowler barrel. I think overcoming the challenges of what it takes to make a flintlock reliably fire in all kinds of weather is a big part of the fun involved. There is a fairly long learning curve compared to a percussion gun, which is far simpler.
Just getting a flintlock to fire is pretty easy, but only part way there. When you do everything properly, you should have a very short lock time, i.e., virtually no delay or hesitation in firing as compared to a percussion or cartridge firearm. Some people think that delay is normal and unavoidable. A short lock time means the gun fires when the sights are aligned with the target, and not a fraction of a second later. That takes well designed locks with good springs, a correctly hardened frizzen, a correctly sized vent in the correct location, a good sharp flint properly installed and of the correct configuration, good dry powder, the correct amount of priming, and more.
I've hunted all day on damp rainy days, frequently checking my pan to make sure my priming was still dry and fluffy, and patted myself on the back for keeping things operational. Then there have been mostly dry days where I felt confident all was well, but when I got back to the truck at the end of the day, my pan powder was a moist black paste. And I wondered how many hours I carried a dead and useless rifle. All it takes to make your gun inert is one snowflake or a drop of water from the trees or brush to land between the pan and barrel.
Even that can be avoided by carrying a small tin of beeswax, and using your pocket knife to lightly caulk that area to shed water or snow. Little details like that, all added together, vastly improve your odds. But when you line up your sights on an animal, you still can't be 100% certain the damn thing will go off... and that's why I love it.
