RE: ml preferance
I have lived in Pennsylvania all my life and we have had a flintlock only whitetail season after Christmas as long as I can remember. Naturally I started my muzzleloading addiction on flinters; we started bow hunting with recurves because that was all there was when I was a kid. I have made a concession of sorts by recently going to a fast twist flinter shooting sabots and conicals. I still hunt and shoot my roundball rifles but I must admit I prefer the extra power for deer.
I have no reason to use crossbows, compounds and inlines; they feel strange in my hands. A recurve feels like it's a part of me and the same goes for flinters. I am happy to see your son has an interest in a traditional rifle. He will enjoy the sport for life.