I forgot about another extant hunting pouch that may be or even probably is 18th century or at the very least is in a style of the period.
Though I certainly realize the problems with documentation of some to many of the hunting pouches illustrated in Madison Grant's book, "The Kentucky Rifle Hunting Pouch," there is one very different pouch and horn set he illustrated that is very similar to the 1776 "Artists Interpretation" portrait of Captain Robert Rogers.
"This 1776 painting is the only known portrait of Robert Rogers from life and from the portrait painter's interpretation."
http://www.npg.org.uk/collections/search/portrait/mw35493/Robert-Rogers
The pouch Madison Grant illustrated is reported to be 7" wide and 8" deep with a 2" wide strap.
Generally I am in very much agreement with Black Hand's fine description of an historically accurate or historically inspired pouch.
The problem as I see it, though, is most of the
very few documented 18th century pouches seem to be what we would call a "Day Pouch," with the exceptions of the pouch mentioned above, the Lemuel Lyman Belt Pouch and perhaps the "Hair Pouch" listed in the 18th century Material Resource Center link. There is documentation that Maryland issued "hair pouches" to some of their troops during the FIW as they had to turn the remaining ones back in to Maryland during 1762. So this pouch perhaps may be more correctly seen as a "military issue" pouch, rather than a civilian hunting pouch.
Now of course a direct "bench made" copy of one of the very few 18th century documented pouches should be considered historically "correct." I would also add that some variation to one of the original pouches should be considered historically correct as long as it is made with 18th century techniques and style.
However, I have to admit I wonder about original 18th century pouches that did not survive the years of use? "Day Pouches" like some/most of the few originals that did survive, were more likely to have survived because they were only used when a person went hunting “for the day” on or near his land and would therefore not require much space for anything but just the bare necessities for shooting the gun. Unless there was imminent danger, most likely these pouches and horns usually stayed inside the cabin or domicile while the man engaged in farming or other activities. There was no reason to have room for more than a few shots for the gun and no reason to have any “survival gear” as we use the term today, though I can see how a flint and steel kit would fit into some of the original pouches along with the other gear.
IOW, I wonder about the original pouches carried by those on the Frontier who went out for longer hunts of a few days to perhaps a couple of weeks, as game got scarce around their area? Perhaps, if not probably, they carried pouches that were a bit larger than the Day Pouches to carry items that were not directly needed to shoot a gun for a few shots? Of course, one could still stay in the general dimensions of the period pouches and add a gusset or even a double pouch to carry more than the minimal items needed to fire the gun for a few shots.
My personal favorite 18th century style pouch I made is actually styled after a Militia Pouch that has enough room for and I made a removable cartridge block for it. When not using the removable cartridge block in the pouch, I have plenty of room for anything I might wish to carry and still get my big “paws” into it to find something.
Gus