Yeah, if you're hunting in Alaska with flinter, you really want something heavy because patched-round balls and even conicals don't have the greatest ballistics. Don't get me wrong - they've reliably killed everything that walks, but you have to know what you're doing. I'd go with something around a .58 or .62 caliber.
As far as the powder and priming goes, black powder comes in a number of granulations. 1F is the coarsest and used for things like cannons (I think there might be a "cannon" grade that's even coarser, but I don't know). The granulations get finer from there. Most people shoot either 2F or 3F as their main charge. Typically, big bores seem like like coarser powders better, but each one is different. I shoot 3F in my .50. 4F powder is for priming ONLY. As the powder is ground finer, its potency increases, so that each grade is about 15% more powerful per equal measure than the one before it.
So, if you're using 100 grains of 2F (a HUGE charge, but easy numbers), you'll need about 85 grains of 3F for equal power. The other thing is that finer grades seem to burn a little cleaner and produce a little less fouling. Not a big deal for hunting because it'll only be one or two shots. But if you're doing lots of target shooting, fouling will build up and you'll need to swab the barrel more often.
Like I said, I use 55 grains of 3F as my main charge. When I'm hunting I just prime with 3F from my main horn so it's less stuff to mess with if I'm reloading in a hurry, but when target shooting I prime my pan with 4F, mostly because I have a can and need to use it up. Some people feel like it ignites more quickly than 3F and works better in priming. I can't tell a difference, but it might be more noticeable if you use 2F as a main charge.
Since we're on the topic, here's a few pics of my rifle and me shooting it.
My .50 Flintlock Tennessee longrifle
My Dad's .40 York, PA style longrifle I built him for Christmas a few years ago
The two together
A couple pics of shooting it. The flash in the pan might be bigger in the pics than normal because we were trying to get dramatic shots. Also, make sure you wear safety glasses (even though I'm not here
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