SO...,
Ask a dozen of us, and you may get a dozen different sets of answers. Here's my slightly different take on what my buddy and brother Marine, Gus, gave you...
Agreed, the adjustable strap is easier to use with a buckle, but there is another method using a leather thong. Either way when the weather gets cold you need a longer strap to go over the clothing.
You do need a closure, as if you move quick or stumble in the woods, stuff tends to "jump out".
Yes this works, BUT none of the bags that I use have such. I prefer that if stuff is to be kept apart, that it is in cinch bags held inside the bag. I also use a small, interior pocket against the back wall of the bag to hold the ball bag, tool, and flints. SO..., I don't have two equal compartments, but I do have a smaller compartment aka a "pocket" so it's only a slightly different idea....
What this means is the bag is sewn, inside out, then reversed for use, so the stitching is in between the sewn pieces of leather. I like this too, but I also like the bag maker to have put in a welt of leather between the two main pieces so that the stitching is even better protected.
Exterior Seam with a contrasting welt... after reversing it looks like this....
View attachment 91580
Well yes a thick leather is nice, BUT for some who use a leather more akin to what was available by the time period and the geography, something like Moose or Elk might not be correct.... and cowhide might not be readily available, and would cost, when a local critter would be "free" except for the labor to make it into leather. So I'd advise that IF a liner is used, that it be sewn as part of the bag, not just as a liner, and..., be attached before sewn with hide glue. NOW to be fair..., some folks like a loose liner, so that if it wears out..., it is more easily replaced. A liner is used for deer hide, ground hog hide, 'coon hide, (or even a goat hide), to reduce the stretching that may happen when heavy objects like a bullet bag or tools are inserted into the bag.
Another requirement..., it holds the gear YOU decide that YOU need to carry to keep your rifle and you in one piece. My bag, for example holds a fire kit, small sharpening stone, and a compass..., some folks only carry gun tools and such.
LD