why hard cast bullets

[PJgunner]

"I can only imagine what it is like to shoot a flint lock. It takes a special person to master one of those."

Not really. If you master just two things, you should be good to go. When you put the powder in the pan, don't have it hard up against the flash hole. You'll get faster ignition if you don't. If it's "agin" the flash hole, it'll act more like a fuse which will delay firing. With the powder slightly away from the hole, the flash will set off the main charge instantly.
The other thing is don't let the flash and smoke coming from the pan make you flinch. That's the hardest part.
Keep your flints sharp and tou shouldn't much problem.
Flinters are lots of fun to shoot. One of these days I'll have to get one to keep my caplocks company.
Oh, I forgot to mention, I am a certified muzzle loader instructor though the Hunter Ed program.
Paul B.