Since the Pouch is full of lead ball, the whole rig is probably made for shooting a muzzleloader. In that case, the likeliest use for the lizard-skin cartridge is to keep the percussion caps (or some black powder - however, it is more likely this hunter would have stored his powder in a powder horn separate from the rig). The Peter's shotgun shell brass boot is likely the powder measure. Muzzle loaders and cartridge loaders have coexisted, and still do, in many parts of the world.
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Odd
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