Smokey Plainsman, if you are seriously interested in flasks and you have any cash left over from that nice Ohio rifle purchase, you might consider ordering a copy of Ray Riling's book, The Powder Flask Book. It was first published in 1953 but as far as I know is still the definitive reference. I think it is out of print, but AbeBooks has 46 used copies for sale. It ain't cheap, but $40 - $60 for a good vintage copy should provide information that's hard to find anywhere else. You'd probably just spend the money on groceries or a new shirt or something if you don't buy the book.
Some ranges and shooting clubs don't allow loading directly from a flask... You need to throw your charge into a separate charger and then put it in your barrel. The idea is that a latent spark from the previous shot might light up your charge (and the powder in your flask) while you are loading. I suppose it could happen...
One other thing to think about is that metals "sweat," or develop condensation on their surface, when exposed to rapid, extreme changes in temperature. For example, if you have been afield some frosty morning, and then come in a heated building to warm up. If you bring your flask in with you, it might sweat a little and introduce some moisture to your powder. One of the several reasons many people continued to use powder horns is that horn doesn't "sweat." Horn is really an ideal material for a powder container.
Best regards,
Notchy Bob