Some good advice here. One thing to consider is not to pre-judge before you start a project.
There's a lot of mis-conception out there stating that, in order to look authentic, your project has to look worn. I always viewed that as inconsistent with the budget and needs of a woodsman running around in the 18th century where materials came dear. I could never imagine an aspiring rifleman walking into Beck or Dickerts or a Christians Spring shop and saying something like..." Oh yeah, make it look beat up. I'll pay extra for that...".
Center your project around function first. When I made this smoothbore for my grandchildren I built the bag around the use of cartridges, so cowhide was fine...
Sometimes all you need to do is buy leather at an event, where sutlers are running around carrying the discards from factories.
When making a bag out of deerskin, I always looked for imperfect hides, dyed them and cured the limp problem by lining them with heavy grade canvas.
The best bag I ever made, and the one that has gone everywhere with me, was one of the first, back in 1981. I was plain buffed suede, without factory shine. Over the years it developed a patina and taught me that, if you are thinking like an eighteenth century craftsman where materials came dear, your improvisation was just as valuable as your material selection.
When you buy, look for integrity in the leather hide first. A good seconds product will go a long way in helping you hit the goal you are looking for and can visualize what you want before you whip out the tools and patterns.
Hope this helps,
Capgun